Source : Webster's Revised Unabridged Dictionary (1913)

Betel nut \Be"tel nut`\
   The nutlike seed of the areca palm, chewed in the East with
   betel leaves (whence its name) and shell lime.

Source : WordNet®

betel nut
     n : seed of betel palm; chewed with leaves of the betel pepper
         and lime as a digestive stimulant and narcotic in
         southeastern Asia [syn: {areca nut}]