Lewis & Short

dē-grassor, āri, v. dep. n. and a.

  1. * I. Neutr., to rush down: deorsum degrassantur aquae, App. de Deo Socr. p. 94.
  2. II. Act., poet. transf., to attack fiercely, to revile: primos duces, Stat. Ach. 1, 406 (cf. grassor with the acc., id. Theb. 8, 5, 4).