I. fifth 1 /fɪfθ/ BrE AmE adjective
[ Language: Old English ; Origin: fifta , from fif 'five' ]
1 . coming after four other things in a series:
in the fifth century
her fifth birthday
2 . fifth wheel American English informal someone who is not wanted in a particular group of people:
They’d made her feel like a fifth wheel.
—fifth pronoun :
I’m planning to leave on the fifth (=the fifth day of the month) .
—fifthly adverb
II. fifth 2 BrE AmE noun [countable]
1 . one of five equal parts of something
2 . American English an amount of alcohol equal to 1/5 of an American ↑ gallon (2), sold in bottles:
a fifth of bourbon