Lewis & Short

fĭmus, i (also fĭmum, i, n., Plin. 28, 17, 70, § 234 sq.; 29, 5, 32, § 101; 30, 9, 23, § 76; Lact. Opif. D. 11, 20: fimo, abl. fem., Apul. Met. 7, p. 200 fin.), m. [Sanscr. dhūmas, smoke; dhū-lis, dust; cf. Gr. θυ-, θύνω, θῦμα, θύος; Lat. sub-fīo, sub-fimen; Germ. Dunst; Engl. dust], that which fertilizes or manures, dung, ordure, excrement (only in the sing., Diom. p. 314 P.; for syn. cf.: stercus, merda, quisquiliae).

  1. I. Lit., Verg. G. 1, 80; Col. 2, 14, 4; 3, 11, 4; Plin. 28, 17, 71, § 235; 30, 9, 23, § 76: caballinus, id. 29, 5, 32, § 102; Liv. 38, 18, 4: fimo si quis aliquem perfuderit, Paul. Sent. 5, 4, 13.
  2. II. Poet. transf. for lutum, dirt, mire, Verg. A. 5, 333 and 358.