The Collaborative International Dictionary of English v.0.48:

Siphonophora \Si`pho*noph"o*ra\, prop. n. pl. [NL., fr. Gr. ???
   a siphon + fe`rein to bear.] (Zool.)
   An order of pelagic Hydrozoa including species which form
   complex free-swimming communities composed of numerous zooids
   of various kinds, some of which act as floats or as swimming
   organs, others as feeding or nutritive zooids, and others as
   reproductive zooids. See Illust. under Physallia, and
   Porpita.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Siphonophora
    n 1: marine colonial hydrozoans [syn: Siphonophora, order
         Siphonophora]