Source : Webster's Revised Unabridged Dictionary (1913)

Pappus \Pap"pus\, n. [L., an old man or grandfather; hence, a
   substance resembling gray hairs, Gr. ?.] (Bot.)
   The hairy or feathery appendage of the achenes of thistles,
   dandelions, and most other plants of the order
   {Composit[ae]}; also, the scales, awns, or bristles which
   represent the calyx in other plants of the same order.

Source : WordNet®

pappus
     n : calyx composed of scales or bristles or featherlike hairs in
         plants of the Compositae such as thistles and dandelions
     [also: {pappi} (pl)]