The Collaborative International Dictionary of English v.0.48:

Thoroughwort \Thor"ough*wort`\, n.
   Same as Boneset.
   [1913 Webster]

WordNet (r) 3.0 (2006):

thoroughwort
    n 1: perennial herb of southeastern United States having white-
         rayed flower heads; formerly used as in folk medicine [syn:
         boneset, agueweed, thoroughwort, Eupatorium
         perfoliatum]