Source : Webster's Revised Unabridged Dictionary (1913)

Upas \U"pas\, n. [Malay p?hn-?pas; p?hn a tree + ?pas poison.]
   1. (Bot.) A tree ({Antiaris toxicaria}) of the Breadfruit
      family, common in the forests of Java and the neighboring
      islands. Its secretions are poisonous, and it has been
      fabulously reported that the atmosphere about it is
      deleterious. Called also {bohun upas}.