The Collaborative International Dictionary of English v.0.48:

24th \24th\ adj.
   1. coming next after the twenty-third in a series

   Syn: twenty-fourth
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

24th
    adj 1: coming next after the twenty-third in position [syn:
           twenty-fourth, 24th]