The Collaborative International Dictionary of English v.0.48:
Sematic \Se*mat"ic\ (s[-e]*m[a^]t"[i^]k), a. [Gr. sh^ma, sh`matos, sign, token.] Significant; ominous; serving as a warning of danger; -- applied esp. to the warning colors or forms of certain animals. [Webster 1913 Suppl.]