brunneous
[f. mod.L. brunneus, = med.L. brunus, f. Teut. brûn BROWN.]

Dark brown. (Chiefly in Entomology.)
1843 HUMPHREYS Brit. Moths I. 137 The hind wings are brunneous grey. 1847 Proc. Berw. Nat. Club II. No. 5. 244 Abdomen..beneath shining brunneous or ferruginous.

OED SECOND EDITION 1989