Lewis & Short

rhūs, rhŏis (also corrupted into roris, Col. 12, 42, 3; abl. rore, id. 9, 13, 5; Pall. Mart. 15, 1), m. (f., Scrib. 142), = ῤοῦς, a bushy shrub, sumach, Plin. 24, 11, 54, § 91; 13, 6, 13, § 55; Cels. 6, 11; Col. 12, 42, 3; Pall. Mart. 15, 1; Scrib. Comp. 111.
Acc. rhun, Plin. 24, 14, 79, § 129: rhum, id. 29, 3, 11, § 50.