[fif.ty] n, pl fifties [ME, fr. fifty, adj., fr. OE fiftig, fr. fiftig, n., group of 50, fr. fif five + -tig group of ten; akin to tien ten] (bef. 12c) 1: five times ten
2. pl: the numbers 50 to 59; specif: the years 50 to 59 in a lifetime or century
3: a 50-dollar bill -- fif.ti.eth adj or n -- fifty adj -- fifty pron, pl in constr -- fif.ty.ish adj