Source : Webster's Revised Unabridged Dictionary (1913)

Arsenical \Ar*sen"ic*al\, a.
   Of or pertaining to, or containing, arsenic; as, arsenical
   vapor; arsenical wall papers.

   {Arsenical silver}, an ore of silver containing arsenic.

Source : WordNet®

arsenical
     adj : relating to or containing arsenic; "arsenic vapor"