Lewis & Short

interŭlus, a, um, adj. dim. [inter], inward, inner (post-class.): nexus, Mart. Cap. 9, § 888: tunica, under-garment, shirt, App. Flor. 9.
Also, subst.: intĕrŭla, ae, f., App. M. 8, p. 205, 16: interulae dilores duae, Vop. Bonos. 15, 8.