Lewis & Short

2. grossus, a, um, adj. [kindred with crassus], thick (late Lat.): virga, Cassiod. Hist. Eccl. 10, 33.
Comp.: vestis grossior, Sulp. Sev. Dal. 1, 21; Vulg. Ezech. 41, 25; 1 Reg. 12, 10; 2 Chron. 10, 10.
Sup., Cassiod. in Psa. 29, 12; cf.: grossus παχύς, Gloss. Philox.
Hence, adv. only comp.: gros-sĭus, more roughly: definire, Aug. de Duab. Anim. 11, 15.