life·time 
/ˈlaɪfˌtaɪm/ noun
plural life·times /ˈlaɪfˌtaɪm/ noun [count] 1 a : the time during which a person is alive
▪ Four editions of the book were printed in his lifetime. [=during his life] ▪ She has had a lifetime of hard work. [=she has worked hard all her life] ▪ a lifetime spent traveling the world ▪ I don't think it will happen in our lifetime. [=the time when we are alive] ▪ She owns enough shoes to last (her) a lifetime. [=to last for the rest of her life] ▪ the thrill of a lifetime [=a great thrill; the most exciting moment or event of a person's life] ▪ This is the opportunity of a lifetime. = This sort of opportunity comes along once in a lifetime. [=this is a very rare opportunity] — often used before another noun ▪ He won a lifetime supply of ice cream. [=free ice cream for the rest of his life] ▪ She was presented with a lifetime achievement award. [=an award for all the work she has done in her life] ▪ a baseball player's lifetime batting average [=batting average measured over a baseball player's full career]
b : a very long time
▪ It would have taken me a lifetime to read all those books. ▪ Childhood seems a lifetime ago now! 2 : the time during which something lasts or is useful
▪ a chemical with a lifetime of only a few minutes ▪ the lifetime of a planet/star/comet
▪ Four editions of the book were printed in his lifetime. [=during his life] ▪ She has had a lifetime of hard work. [=she has worked hard all her life] ▪ a lifetime spent traveling the world ▪ I don't think it will happen in our lifetime. [=the time when we are alive] ▪ She owns enough shoes to last (her) a lifetime. [=to last for the rest of her life] ▪ the thrill of a lifetime [=a great thrill; the most exciting moment or event of a person's life] ▪ This is the opportunity of a lifetime. = This sort of opportunity comes along once in a lifetime. [=this is a very rare opportunity] — often used before another noun ▪ He won a lifetime supply of ice cream. [=free ice cream for the rest of his life] ▪ She was presented with a lifetime achievement award. [=an award for all the work she has done in her life] ▪ a baseball player's lifetime batting average [=batting average measured over a baseball player's full career]
b : a very long time
▪ It would have taken me a lifetime to read all those books. ▪ Childhood seems a lifetime ago now!
▪ a chemical with a lifetime of only a few minutes ▪ the lifetime of a planet/star/comet
