The Collaborative International Dictionary of English v.0.48:

Suasion \Sua"sion\, n. [L. suasio, fr. suadere, suasum, to
   advise, persuade, fr. suadus persuading, persuasive; akin to
   suavis sweet: cf. OF. suasion. See Suave, and cf.
   Dissuade, Persuade.]
   The act of persuading; persuasion; as, moral suasion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

suasion
    n 1: the act of persuading (or attempting to persuade);
         communication intended to induce belief or action [syn:
         persuasion, suasion] [ant: dissuasion]