[nine.ty] n, pl nineties [ME ninety, adj., fr. OE nigontig, short for hundnigontig, fr. hundnigontig, n., group of 90, fr. hund-, lit., hundred + nigon nine + -tig group of 10; akin to OE tien ten] (bef. 12c) 1: nine times ten
2. pl: the numbers 90 to 99; specif: the years 90 to 99 in a lifetime or century -- nine.ti.eth adj or n -- ninety adj -- ninety pron, pl in constr