The Collaborative International Dictionary of English v.0.48:

Ailantus \Ai*lan"tus\, n. [From aylanto, i. e., tree of heaven,
   the name of the tree in the Moluccas.] (Bot.)
   A genus of beautiful trees, natives of the East Indies. The
   tree imperfectly di[oe]cious, and the staminate or male plant
   is very offensive when blossom.
   [1913 Webster]