WordNet sense 1 (of the remaining member of a pair, of socks e.g.):

odd, unpaired, unmated

WordNet sense 2 (either not matched or unsuitably matched):

mismatched

WordNet sense 3 (eminent beyond or above comparison):

matchless, nonpareil, one, peerless, unrivaled, unrivalled, unmatchable

WordNet sense 4 (such that comparison is impossible; unsuitable for comparison or lacking features that can be compared):

incomparable, uncomparable