The Collaborative International Dictionary of English v.0.48:

3 \3\ adj.
   1. one more than two; denoting a quantity consisting of three
      items or units; -- representing the number three as an
      Arabic numeral.

   Syn: three, iii
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

3
    adj 1: being one more than two [syn: three, 3, iii]
    n 1: the cardinal number that is the sum of one and one and one
         [syn: three, 3, III, trio, threesome, tierce,
         leash, troika, triad, trine, trinity, ternary,
         ternion, triplet, tercet, terzetto, trey, deuce-
         ace]