Source : WordNet®

believably
     adv 1: in a believable manner; "he acted believably sincere" [ant:
            {unbelievably}, {incredibly}]
     2: easy to believe on the basis of available evidence; "he
        talked plausibly before the committee"; "he will probably
        win the election" [syn: {credibly}, {plausibly}, {probably}]
        [ant: {incredibly}]