The Collaborative International Dictionary of English v.0.48:

500 \500\ adj.
   1. one more than four hundred ninety-nine; five times one
      hundred; denoting a quantity consisting of five hundred
      items or units; -- representing the number five hundred as
      Arabic numerals

   Syn: five hundred, d
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

500
    adj 1: denoting a quantity consisting of 500 items or units
           [syn: five hundred, 500, d]
    n 1: the cardinal number that is the product of one hundred and
         five [syn: five hundred, 500, D]