The Collaborative International Dictionary of English v.0.48:

Felwort \Fel"wort`\, n. [Probably a corruption of fieldwort.]
   (Bot.)
   A European herb (Swertia perennis) of the Gentian family.
   [1913 Webster]

WordNet (r) 3.0 (2006):

felwort
    n 1: gentian of Europe and China having creamy white flowers
         with fringed corollas [syn: felwort, gentianella
         amarella]