Source : Webster's Revised Unabridged Dictionary (1913)

Excusable \Ex*cus"a*ble\a. [L. excusabilis: cf. F. excusable.
   See {Excuse}.]
   That may be excused, forgiven, justified, or acquitted of
   blame; pardonable; as, the man is excusable; an excusable
   action. -- {Ex*cus"a*ble*ness}, n. -- {Ex*cus"a*bly}, adv.

         The excusableness of my dissatisfaction. --Boyle.

Source : WordNet®

excusably
     adv : in an excusable manner or to an excusable degree; "he was
           excusably late" [syn: {forgivably}, {pardonably}] [ant:
            {inexcusably}, {inexcusably}, {inexcusably}]