opposable

from WordNet (r) 3.0 (2006)

opposable
    adj 1: capable of being placed opposite to something; "the thumb
           is opposable to the forefinger" [syn: {opposable},
           {apposable}] [ant: {unopposable}]

from The Collaborative International Dictionary of English v.0.48

Opposable \Op*pos"a*ble\, a.
   1. Capable of being opposed or resisted.
      [1913 Webster]

   2. Capable of being placed opposite something else; as, the
      thumb is opposable to the forefinger.
      [1913 Webster]