The Collaborative International Dictionary of English v.0.48:

Warrantable \War"rant*a*ble\, a.
   Authorized by commission, precept, or right; justifiable;
   defensible; as, the seizure of a thief is always warrantable
   by law and justice; falsehood is never warrantable.
   [1913 Webster]

         His meals are coarse and short, his employment
         warrantable, his sleep certain and refreshing. --South.
   [1913 Webster] -- War"rant*a*ble*ness, n. --
   War"rant*bly, adv.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "warrantable":
   admissible, allowable, balanced, condonable, defensible, deserved,
   dispensable, due, equitable, even, evenhanded, excusable,
   exemptible, expiable, fair, fair and square, fit, forgivable, good,
   inoffensive, just, justifiable, justified, lawful, legal,
   legitimate, legitimized, level, licit, meet, meet and right,
   merited, pardonable, permissible, proper, reasonable, remissible,
   right, right and proper, rightful, sanctionable, square, tenable,
   unobjectionable, venial, vindicable, warranted