The Collaborative International Dictionary of English v.0.48:

Confirmable \Con*firm"a*ble\, a.
   That may be confirmed.
   [1913 Webster]

WordNet (r) 3.0 (2006):

confirmable
    adj 1: capable of being tested (verified or falsified) by
           experiment or observation [syn: confirmable,
           verifiable, falsifiable]