Entry 3 senses · 2 variants Webster, 1913 Ninety /nīn'-tē/ · Nine·ty · IPA /ˈnaɪn.di/ a. n. 01 a. Nine times ten; eighty-nine and one more; as, ninety men. 1. Nine times ten; eighty-nine and one more; as, ninety men. 02 n. The sum of nine times ten; the number greater by a unit than eighty-nine; ninety units or objects. pl. Nineties 1. The sum of nine times ten; the number greater by a unit than eighty-nine; ninety units or objects. 2. A symbol representing ninety units, as 90 or xc.