1back 
/ˈbæk/ noun
plural backs /ˈbæk/ noun [count] 1 a : the rear part of the body : the part of the body that is opposite to the stomach and chest and that goes from the neck to the top of the legs
▪ She was carrying her little daughter on her back. ▪ He injured his back. = He suffered a back injury. ▪ She has a pain in the small of her back. ▪ an aching back ▪ I slapped/patted him on his/the back to congratulate him. ▪ He broke his back [=spine] in a fall. ▪ She stabbed/shot him in the back. ▪ He was handcuffed with his hands behind his back. — see picture at human
b : the part of an animal that is like a person's back
▪ a bird with a spotted back ▪ riding on the back of a horse/donkey/camel — see also horseback 2 a : the side or surface of something that is opposite the front or face : the rear side or surface of something — usually singular ▪ the back of the head ▪ the back of a mirror/spoon ▪ the back of the hand/leg/foot ▪ The book has fallen down the back of the couch.
b : the side or surface of something (such as a piece of paper) that is not usually used or seen first — usually singular ▪ She wrote something on the back of an envelope. ▪ He signed his name on the back of the check.
c : a place, position, or area that is at or near the rear of something — usually singular ▪ He put the letter in the back of the drawer. ▪ The kitchen is at/in the back of the house and the living room is at/in the front. ▪ Since our plane was leaving soon we were moved to the front of the line while others remained at the back. ▪ Please move to the back of the elevator to make room for others. 3 : the part of a chair or seat that supports a person's back
▪ a comfortable chair with a padded back 4 a : the section of a book, magazine, etc., that includes the last pages — usually singular ▪ There is an index in the back of the book.
b : the part of a book's cover that can be seen when the book is on a shelf
▪ The title of the book is shown on its back. [=spine] 5 sports : a player in some games (such as soccer and American football) who is positioned behind the front line of players
▪ a defensive back — see also fullback, halfback, quarterback, running back
▪ She was carrying her little daughter on her back. ▪ He injured his back. = He suffered a back injury. ▪ She has a pain in the small of her back. ▪ an aching back ▪ I slapped/patted him on his/the back to congratulate him. ▪ He broke his back [=spine] in a fall. ▪ She stabbed/shot him in the back. ▪ He was handcuffed with his hands behind his back. — see picture at human
b : the part of an animal that is like a person's back
▪ a bird with a spotted back ▪ riding on the back of a horse/donkey/camel — see also horseback
b : the side or surface of something (such as a piece of paper) that is not usually used or seen first — usually singular ▪ She wrote something on the back of an envelope. ▪ He signed his name on the back of the check.
c : a place, position, or area that is at or near the rear of something — usually singular ▪ He put the letter in the back of the drawer. ▪ The kitchen is at/in the back of the house and the living room is at/in the front. ▪ Since our plane was leaving soon we were moved to the front of the line while others remained at the back. ▪ Please move to the back of the elevator to make room for others.
▪ a comfortable chair with a padded back
b : the part of a book's cover that can be seen when the book is on a shelf
▪ The title of the book is shown on its back. [=spine]
▪ a defensive back — see also fullback, halfback, quarterback, running back
a pat on the back — see 1pat
a stab in the back — see 1stab
at/in the back of your mind
: in the part of your mind where thoughts and memories are kept — used to describe ideas, memories, etc., that someone has but that are not usually thought about or not perfectly remembered ▪ The thought of retiring and moving out into the country has been in the back of her mind for many years, and now she's finally doing it. ▪ Somewhere in the back of my mind I knew I'd met him before.
back is to/against the wall
◊When your back is to/against the wall or you have your back to/against the wall you are in a bad position in which you are forced to do something in order to avoid failure.
▪ With our backs to the wall we made a last desperate effort to finish the project on time. ▪ We knew that with so little time and money left to finish the project we had our backs to the wall.
▪ With our backs to the wall we made a last desperate effort to finish the project on time. ▪ We knew that with so little time and money left to finish the project we had our backs to the wall.
back to back 1 : with backs opposite or against each other
▪ The soldiers stood back to back. 2 : happening one after the other
▪ She won the annual competition two times back to back. [=in a row] ▪ He's had two victories back to back. ▪ I've scheduled two appointments back to back. — see also back-to-back
▪ The soldiers stood back to back.
▪ She won the annual competition two times back to back. [=in a row] ▪ He's had two victories back to back. ▪ I've scheduled two appointments back to back. — see also back-to-back
back to front
of a piece of clothing : with the back where the front should be
▪ He accidentally put the sweater on back to front. [=front to back, backwards]
▪ He accidentally put the sweater on back to front. [=front to back, backwards]
behind someone's back
: without someone's knowledge : in secret
▪ You shouldn't gossip about people behind their back(s). ▪ If you have something to say, why not say it to my face instead of whispering it behind my back?! ▪ She went behind his back and spoke directly to his supervisor.
▪ You shouldn't gossip about people behind their back(s). ▪ If you have something to say, why not say it to my face instead of whispering it behind my back?! ▪ She went behind his back and spoke directly to his supervisor.
break the back of
: to get control of (something you are trying to stop or defeat) : to greatly weaken or subdue (something)
▪ He says the government's new policies will break the back of inflation.
▪ He says the government's new policies will break the back of inflation.
eyes in the back of your head — see 1eye
get your back up
: to become angry or annoyed and want to fight or argue
▪ He gets his back up and becomes defensive whenever someone questions his work. — compare put someone's back up (below)
▪ He gets his back up and becomes defensive whenever someone questions his work. — compare put someone's back up (below)
have someone's back — see watch someone's back (below)
in back
: in an area at the back of something
▪ There was only room for one passenger in front. The rest of us sat in back. [=in the back]
▪ There was only room for one passenger in front. The rest of us sat in back. [=in the back]
in back of
chiefly US : directly behind (something or someone)
▪ There's a small yard in back of the house.
▪ There's a small yard in back of the house.
on the back of 1 : because of (something)
▪ Profits have increased on the back of [=on the strength of] improved international sales. 2 disapproving : by using the efforts of (other people)
▪ The company has achieved record profits on the back of cheap labor.
▪ Profits have increased on the back of [=on the strength of] improved international sales.
▪ The company has achieved record profits on the back of cheap labor.
on/off your back
◊Someone who is always or frequently criticizing you or telling you what to do is on your back and won't get off your back.
▪ He says his wife is always on his back about doing chores around the house. ▪ Get off my back! I'm working as hard as I can! ▪ My boss is always criticizing me. I wish I knew some way to get him off my back.
▪ He says his wife is always on his back about doing chores around the house. ▪ Get off my back! I'm working as hard as I can! ▪ My boss is always criticizing me. I wish I knew some way to get him off my back.
on your back
◊If you are (flat) on your back you are lying with your back against the ground, on a bed, etc.
▪ The accident left him (lying) flat on his back (in bed) for two weeks. This phrase is sometimes used figuratively. ▪ The stock market has been flat on its back [=has been doing very poorly] in recent weeks.
▪ The accident left him (lying) flat on his back (in bed) for two weeks. This phrase is sometimes used figuratively. ▪ The stock market has been flat on its back [=has been doing very poorly] in recent weeks.
out back (US) or chiefly Brit out the back or round the back
: in the area behind something (such as a building)
▪ In my youth we didn't have a toilet in the house but there was one out back.
▪ In my youth we didn't have a toilet in the house but there was one out back.
put someone's back up
: to offend or annoy someone : to make someone angry or ready to argue
▪ I don't want to question his decision because that will just put his back up. — compare get your back up (above)
▪ I don't want to question his decision because that will just put his back up. — compare get your back up (above)
put your back into
: to work very hard at (something) : to put a lot of effort into (something)
▪ If you want to get that floor clean you'll have to put your back into it. ▪ You'll really have to put your back into this project if you want it to succeed.
▪ If you want to get that floor clean you'll have to put your back into it. ▪ You'll really have to put your back into this project if you want it to succeed.
scratch someone's back — see 1scratch
see the back of
◊In British English, to be glad/happy (etc.) to see the back of someone is to be glad to see someone finally going away.
▪ He's done nothing but make trouble and I'll be glad to see the back of him! [=I'll be glad when he has gone]
▪ He's done nothing but make trouble and I'll be glad to see the back of him! [=I'll be glad when he has gone]
stab (someone) in the back — see 2stab
the shirt off your back — see shirt
turn your back
: to turn so that you are facing away from someone
▪ He turned his back and walked away from me. — often + on ▪ He turned his back on me and walked away. — often used figuratively ▪ His former supporters have turned their backs on him. [=have abandoned him]
▪ He turned his back and walked away from me. — often + on ▪ He turned his back on me and walked away. — often used figuratively ▪ His former supporters have turned their backs on him. [=have abandoned him]
watch someone's back or have someone's back
: to protect someone who is doing something that is dangerous or risky
▪ The police officer's partner always watches his back. ▪ Don't worry, I've got your back.
▪ The police officer's partner always watches his back. ▪ Don't worry, I've got your back.
watch your back
◊If people tell you to watch your back, they are telling you to be careful.
▪ I hear the boss is in a bad mood this morning, so you'd better watch your back.
▪ I hear the boss is in a bad mood this morning, so you'd better watch your back.
— back·less /ˈbækləs/ adjective
▪ a backless evening gown
/ˈbækləs/ adjective ▪ a backless evening gown
