Source : Webster's Revised Unabridged Dictionary (1913)

Unnatural \Un*nat"u*ral\ (?; 135), a.
   Not natural; contrary, or not conforming, to the order of
   nature; being without natural traits; as, unnatural crimes.

   Syn: See {Factitious}. -- {Un*nat"u*ral*ly}, adv. --
        {Un*nat"u*ral*ness}, n.

Source : WordNet®

unnatural
     adj 1: not in accordance with or determined by nature; contrary to
            nature; "an unnatural death"; "the child's unnatural
            interest in death" [ant: {natural}]
     2: speaking or behaving in an artificial way to make an
        impression [syn: {affected}] [ant: {unaffected}]
     3: distorted and unnatural in shape or size; abnormal and
        hideous; "tales of grotesque serpents eight fathoms long
        that churned the seas"; "twisted into monstrous shapes"
        [syn: {grotesque}, {monstrous}]