The Collaborative International Dictionary of English v.0.48:

Tormentil \Tor"men*til\, n. [F. tormentille; cf. Pr., It., & NL.
   tormentilla, Sp. tormentila; all fr. L. tormentum pain. So
   called because it is said to allay pain. See Torment.]
   (Bot.)
   A rosaceous herb (Potentilla Tormentilla), the root of
   which is used as a powerful astringent, and for alleviating
   gripes, or tormina, in diarrhea.
   [1913 Webster]