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.]