Lewis & Short

soccŭlus, i, m. dim. [soccus], a small soccus, Sen. Ben. 2, 12, 1; Suet. Vit. 2 fin.; Plin. 9, 35, 56, § 114.
Of the sock worn by comic actors (v. soccus, II.), Plin. Ep. 9, 7, 3; Quint. 10, 2, 22.