The Collaborative International Dictionary of English v.0.48:

Ihlang-ihlang \Ih*lang`-ih*lang"\, n. [Malayan, flower of
   flowers.]
   A rich, powerful, perfume, obtained from the volatile oil of
   the flowers of Canada odorata, an East Indian tree. [Also
   written ylang-ylang.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ylang-ylang \Y*lang`-y*lang"\, n.
   See Ihlang-ihlang.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

ylang-ylang
    n 1: evergreen Asian tree with aromatic greenish-yellow flowers
         yielding a volatile oil; widely grown in the tropics as an
         ornamental [syn: ilang-ilang, ylang-ylang, Cananga
         odorata]