1fifth 
/ˈfɪθ, ˈfɪfθ/ noun
plural fifths /ˈfɪθ, ˈfɪfθ/ noun 1 [singular] : number five in a series
▪ The bill is due on the fifth of each month. 2 [count] : one of five equal parts of something
▪ She donated a fifth of her income to charity. 3 [count] : a unit of measure for alcoholic liquor that is equal to one fifth of a U.S. gallon (approximately 750 ml) ; also : a bottle that holds this amount of liquor
▪ bought a fifth of whiskey
▪ The bill is due on the fifth of each month.
▪ She donated a fifth of her income to charity.
▪ bought a fifth of whiskey
take/plead the Fifth
chiefly US : to refuse to answer questions in a court of law because your answers might be harmful to you or might show that you have committed a crime
▪ When called to testify, he took the Fifth. — often used figuratively ▪ He took the Fifth [=he refused to answer] when his wife asked him where he'd spent the night. ◊The phrase take/plead the Fifth refers to the Fifth Amendment of the U.S. Constitution, which says that citizens of the U.S. cannot be required to give testimony that could be used against them in a court of law.
▪ When called to testify, he took the Fifth. — often used figuratively ▪ He took the Fifth [=he refused to answer] when his wife asked him where he'd spent the night. ◊The phrase take/plead the Fifth refers to the Fifth Amendment of the U.S. Constitution, which says that citizens of the U.S. cannot be required to give testimony that could be used against them in a court of law.
