The Collaborative International Dictionary of English v.0.48:

philadelphus \philadelphus\ n.
   Any of various chiefly deciduous ornamental shrubs of the
   genus Philadelphus having white sweet-scented flowers,
   single or in clusters; it is widely grown in temperate
   regions.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

philadelphus
    n 1: any of various chiefly deciduous ornamental shrubs of the
         genus Philadelphus having white sweet-scented flowers,
         single or in clusters; widely grown in temperate regions