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]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]