Wordnet 3.0
ADVERB (2)
1. 
 in a believable manner; 
- Example: "he acted believably sincere"2. 
 easy to believe on the basis of available evidence; 
- Example: "he talked plausibly before the committee"- Example: "he will probably win the election"[syn: credibly, believably, plausibly, probably]
WordNet (r) 3.0 (2006):
believably
    adv 1: in a believable manner; "he acted believably sincere"
           [ant: implausibly, improbably, incredibly,
           unbelievably]
    2: easy to believe on the basis of available evidence; "he
       talked plausibly before the committee"; "he will probably win
       the election" [syn: credibly, believably, plausibly,
       probably] [ant: implausibly, improbably, incredibly,
       unbelievably]