Sardonic

a.
  1. Forced; unnatural; insincere; hence, derisive, mocking, malignant, or bitterly sarcastic; -- applied only to a laugh, smile, or some facial semblance of gayety.
  2. Sardonic grin or Sardonic laugh ,
    an old medical term for a spasmodic affection of the muscles of the face, giving it an appearance of laughter.

a.
  1. Of, pertaining to, or resembling, a kind of linen made at Colchis.