1. 
[syn: credibly, believably, plausibly, probably]
The Collaborative International Dictionary of English v.0.48:
Plausibly \Plau"si*bly\, adv.
   1. In a plausible manner.
      [1913 Webster]
   2. Contentedly, readily. [Obs.]
      [1913 Webster]
            The Romans plausibly did give consent. --Shak.
      [1913 Webster]
WordNet (r) 3.0 (2006):
plausibly
    adv 1: 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]