The Collaborative International Dictionary of English v.0.48:

Forgivable \For*giv"a*ble\, a.
   Capable of being forgiven; pardonable; venial. --Sherwood.
   [1913 Webster]

WordNet (r) 3.0 (2006):

forgivable
    adj 1: easily excused or forgiven; "a venial error" [syn:
           excusable, forgivable, venial]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "forgivable":
   admissible, allowable, condonable, defensible, dispensable,
   excusable, exemptible, expiable, inoffensive, justifiable,
   legitimate, pardonable, reasonable, remissible, unobjectionable,
   venial, vindicable, warrantable