The Collaborative International Dictionary of English v.0.48:

costusroot \costusroot\ n.
   an annual herb (Saussurea costus) of the eastern Himalayas
   (Kashmir) having purple florets and a fragrant root that
   yields a volatile oil used in perfumery and for preserving
   furs.

   Syn: Saussurea costus, Saussurea lappa.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

costusroot
    n 1: annual herb of the eastern Himalayas (Kashmir) having
         purple florets and a fragrant root that yields a volatile
         oil used in perfumery and for preserving furs [syn:
         costusroot, Saussurea costus, Saussurea lappa]