Source : Webster's Revised Unabridged Dictionary (1913)

Tentacle \Ten"ta*cle\, n. [NL. tentaculum, from L. tentare to
   handle, feel: cf. F. tentacule. See {Tempt}.] (Zo["o]l.)
   A more or less elongated process or organ, simple or
   branched, proceeding from the head or cephalic region of
   invertebrate animals, being either an organ of sense,
   prehension, or motion.

   {Tentacle sheath} (Zo["o]l.), a sheathlike structure around
      the base of the tentacles of many mollusks.

Source : WordNet®

tentacle
     n 1: something that acts like a tentacle in its ability to grasp;
          "caught in the tentacles of organized crime"
     2: any of various elongated tactile or prehensile flexible
        organs that occur on the head or near the mouth in many
        animals used for feeling or grasping or locomotion