XVIII

from WordNet (r) 3.0 (2006)

xviii
    adj 1: being one more than seventeen [syn: {eighteen}, {18},
           {xviii}]
    n 1: the cardinal number that is the sum of seventeen and one
         [syn: {eighteen}, {18}, {XVIII}]

from The Collaborative International Dictionary of English v.0.48

xviii \xviii\, adj.
   The Roman number symbolizing the value eighteen.

   Syn: eighteen, 18.
        [WordNet 1.5]

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