Source : Webster's Revised Unabridged Dictionary (1913)

Cowan \Cow"an\ (kou"an), n. [Cf. OF. couillon a coward, a
   cullion.]
   One who works as a mason without having served a regular
   apprenticeship. [Scot.]

   Note: Among Freemasons, it is a cant term for pretender,
         interloper.