The Collaborative International Dictionary of English v.0.48:
Affirmable \Af*firm"a*ble\, a. Capable of being affirmed, asserted, or declared; -- followed by of; as, an attribute affirmable of every just man. [1913 Webster]WordNet (r) 3.0 (2006):
affirmable adj 1: capable of being affirmed or asserted; "a quality affirmable of every member of the family" [syn: affirmable, assertable]