fif ‧ ty /ˈfɪfti/ BrE AmE number , noun
[ Language: Old English ; Origin: fiftig , from fif 'five' ]
1 . the number 50
2 . the fifties [plural] ( also the '50s , the 1950s ) the years between 1950 and 1959:
Standards of living rose in the fifties.
the early/mid/late fifties
The play was written in the late fifties.
3 . be in your fifties to be aged between 50 and 59
early/mid/late fifties
He must be in his early fifties by now.
4 . in the fifties if the temperature is in the fifties, it is between 50 degrees and 59 degrees
in the low/mid/high fifties
sunny, with temperatures in the mid fifties
5 . [countable] a piece of paper money that is worth 50 dollars or 50 pounds:
I can give you five tens for that fifty if you want.
—fiftieth adjective :
her fiftieth birthday