Source : Webster's Revised Unabridged Dictionary (1913)

Unpaired \Un*paired\, a.
   Not paired; not suited or matched.

         And minds unpaired had better think alone. --Crabbe.

Source : WordNet®

unpaired
     adj : of the remaining member of a pair, of socks e.g. [syn: {odd},
            {unmatched}, {unmated}]