The Collaborative International Dictionary of English v.0.48:

Kapok \Ka*pok"\, n. [Prob. fr. the native name.] (Bot.)
   A silky wool derived from the seeds of Ceiba pentandra
   (syn. Eriodendron anfractuosum), a bombaceous tree of the
   East and West Indies.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Ceiba pentandra
    n 1: massive tropical tree with deep ridges on its massive trunk
         and bearing large pods of seeds covered with silky floss;
         source of the silky kapok fiber [syn: kapok, ceiba
         tree, silk-cotton tree, white silk-cotton tree,
         Bombay ceiba, God tree, Ceiba pentandra]