Source : Webster's Revised Unabridged Dictionary (1913)

Pachak \Pa*chak"\, n. (Bot.)
   The fragrant roots of the {Saussurea Costus}, exported from
   India to China, and used for burning as incense. It is
   supposed to be the costus of the ancients. [Written also
   {putchuck}.]

Source : WordNet®

Saussurea costus
     n : 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 lappa}]