Lewis & Short

sellāris, e, adj. [sella], of or belonging to a seat (post-class.): gestatio, in a sedan, Cael. Aur. Tard. 1, 4, 92: jumenta, furnished with saddles, used for riding, Veg. 2, 28, 34; 6, 7, 5.
Subst.: sellāris, is, m., a saddlehorse, Vit. Caes. Arel. 2, 2, 20.