The Collaborative International Dictionary of English v.0.48:

xxii \xxii\, adj.
   The Roman number representing twenty-two.

   Syn: twenty-two, 22.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

xxii
    adj 1: being two more than twenty [syn: twenty-two, 22,
           xxii]
    n 1: the cardinal number that is the sum of twenty-one and one
         [syn: twenty-two, 22, XXII]