Source : Webster's Revised Unabridged Dictionary (1913)

Beggar's lice \Beg"gar's lice`\ (Bot.)
   The prickly fruit or seed of certain plants (as some species
   of {Echinospermum} and {Cynoglossum}) which cling to the
   clothing of those who brush by them.

Source : WordNet®

beggar's lice
     n 1: Eurasian and North American plants having small prickly
          nutlets that stick to clothing [syn: {beggar lice}]
     2: any of various tropical and subtropical plants having
        trifoliate leaves and rough sticky pod sections or loments
        [syn: {tick trefoil}, {beggar lice}]