The Collaborative International Dictionary of English v.0.48:

23 \23\ adj.
   1. one more than twenty-two; denoting a quantity consisting
      of twenty-three items or units; -- representing the number
      twenty-three as Arabic numerals

   Syn: twenty-three, xxiii
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

23
    adj 1: being three more than twenty [syn: twenty-three, 23,
           xxiii]
    n 1: the cardinal number that is the sum of twenty-two and one
         [syn: twenty-three, 23, XXIII]