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]