Source : Webster's Revised Unabridged Dictionary (1913)

Swearer \Swear"er\, n.
   1. One who swears; one who calls God to witness for the truth
      of his declaration.

   2. A profane person; one who uses profane language.

            Then the liars and swearers are fools. --Shak.

Source : WordNet®

swearer
     n 1: someone who uses profanity
     2: someone who takes a solemn oath