The Collaborative International Dictionary of English v.0.48:

Syringa \Sy*rin"ga\, n. [NL., fr. Gr. ?, ?, a shepherd's pipe,
   tube. Cf. Syringe.] (Bot.)
   (a) A genus of plants; the lilac.
   (b) The mock orange; -- popularly so called because its stems
       were formerly used as pipestems.
       [1913 Webster]

WordNet (r) 3.0 (2006):

syringa
    n 1: large hardy shrub with showy and strongly fragrant creamy-
         white flowers in short terminal racemes [syn: mock
         orange, syringa, Philadelphus coronarius]
    2: genus of Old World shrubs or low trees having fragrant
       flowers in showy panicles: lilacs [syn: Syringa, genus
       Syringa]