fifty /ˈfɪfti/number 1noun 2forms 2phrases 1 number1 •the number 50It was just fifty children that Selene bore to Endymion. Are not the innumerable waves typified by the fifty Nereïds? And did not Priam have fifty sons and fifty daughters? — 1924 noun2 •A banknote or coin with a denomination of 50.Do you want small bills or are fifties OK? •A batsman's score of at least 50 runs and less than 100 runs. formsfifties · fifty-somethings Phrases with fifty fifty-cent tourA fast and general introduction to a place.