The Collaborative International Dictionary of English v.0.48:

Betel \Be"tel\ (b[=e]"t'l), n. [Pg., fr. Tamil ve[.t][.t]ilei,
   prop. meaning, a mere leaf.] (Bot.)
   A species of pepper (Piper betle), the leaves of which are
   chewed, with the areca or betel nut and a little shell lime,
   by the inhabitants of the East Indies. It is a woody climber
   with ovate many-nerved leaves.
   [1913 Webster]

WordNet (r) 3.0 (2006):

betel
    n 1: Asian pepper plant whose dried leaves are chewed with betel
         nut (seed of the betel palm) by southeast Asians [syn:
         betel, betel pepper, Piper betel]