Source : Webster's Revised Unabridged Dictionary (1913)

Lilac \Li"lac\ (l[imac]"lak), n. [Also {lilach}.] [Sp. lilac,
   lila, Ar. l[=i]lak, fr. Per. l[=i]laj, l[=i]lanj, l[=i]lang,
   n[=i]laj, n[=i]l, the indigo plant, or from the kindred
   l[=i]lak bluish, the flowers being named from the color. Cf.
   {Anil}.]
   1. (Bot.) A shrub of the genus {Syringa}. There are six
      species, natives of Europe and Asia. {Syringa vulgaris},
      the common lilac, and {S. Persica}, the Persian lilac, are
      frequently cultivated for the fragrance and beauty of
      their purplish or white flowers. In the British colonies
      various other shrubs have this name.

   2. A light purplish color like that of the flower of the
      purplish lilac.

   {California lilac} (Bot.), a low shrub with dense clusters of
      purplish flowers ({Ceanothus thyrsiflorus}).

Source : WordNet®

Syringa vulgaris
     n : large European lilac naturalized in North America having
         heart-shaped ovate leaves and large panicles of highly
         fragrant lilac or white flowers [syn: {common lilac}]