1. [n]  the cardinal number that is the product of ten and nine
2. [adj]  being ten more than eighty

NINETY is a 6 letter word that starts with N.

1. \Nine"ty\, a. [See {Nine}, and cf. {Forty}.]
   Nine times ten; eighty-nine and one more; as, ninety men.
   
   

2. \Nine"ty\, n.; 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.