The Collaborative International Dictionary of English v.0.48:

Upas \U"pas\ ([=u]"p[.a]s), n. [Malay p[=u]hn-[=u]pas; p[=u]hn a
   tree + [=u]pas poison.]
   [1913 Webster]
   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.
      [1913 Webster]
      [1913 Webster]

   2. A virulent poison used in Java and the adjacent islands
      for poisoning arrows. One kind, upas antiar, is derived
      from the upas tree (Antiaris toxicaria). Upas tieute
      is prepared from a climbing plant (Strychnos Tieute).
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bohun upas \Bo"hun u"pas\
   See Upas.
   [1913 Webster]