The Collaborative International Dictionary of English v.0.48:

Gromwell \Grom"well\, n. [Called also gromel, grommel, graymill,
   and gray millet, all prob. fr. F. gr?mil, cf. W. cromandi.]
   (Bot.)
   A plant of the genus Lithospermum (L. arvense), anciently
   used, because of its stony pericarp, in the cure of gravel.
   The German gromwell is the Stellera. [Written also
   gromill.]
   [1913 Webster]