The Collaborative International Dictionary of English v.0.48:

boson \bo"son\ (b[=o]"s'n), n.
   See Boatswain. [Obs.] [Also spelled bosun.] --Dryden.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

bosun \bosun\ n.
   a petty officer on a merchant ship who controls the work of
   other seamen; a contraction of boatswain. [Also spelled
   bo'sun.]

   Syn: boatswain, bos'n, bo's'n, bo'sun, boson.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

bosun
    n 1: a petty officer on a merchant ship who controls the work of
         other seamen [syn: boatswain, bos'n, bo's'n, bosun,
         bo'sun]