[six.ty] n, pl sixties [ME, fr. sixty, adj., fr. OE siextig, n., group of sixty, fr. siex six + -tig group of ten; akin to OE tien ten] (14c) 1: six times ten
2. pl: the numbers 60 to 69; specif: the years 60 to 69 in a lifetime or century -- six.ti.eth adj or n -- sixty adj -- sixty pron, pl in constr -- six.ty.ish adj