The Collaborative International Dictionary of English v.0.48:

Canonicals \Ca*non"ic*als\, n. pl.
   The dress prescribed by canon[2] to be worn by a clergyman
   when officiating. Sometimes, any distinctive professional
   dress.
   [1913 Webster]

   Full canonicals, the complete costume of an officiating
      clergyman or ecclesiastic.

The Devil's Dictionary (1881-1906):

CANONICALS, n.  The motley worm by Jesters of the Court of Heaven.