Lewis & Short

soccus, i, m.

  1. I. A kind of low-heeled, light shoe, worn by the Greeks; a slipper, sock, Plaut. Trin. 3, 2, 94; id. Ep. 5, 2, 60; id. Bacch. 2, 3, 98; id. Pers. 1, 3, 44; id. Cist. 4, 2, 29: soccos, quibus indutus esset, Cic. de Or. 3, 32, 127; id. Rab. Post. 10, 27; Cat. 61, 10 et saep.
    When worn by Romans they were a sign of effeminacy, Suet. Calig. 52; Sen. Ben. 2, 12, 1; Plin. 37, 2, 6, § 17.
    The soccus was worn especially by comic actors (the cothurnus, on the contrary, by tragic actors).
    Hence,
  2. II. Transf., comedy (as cothurnus, tragedy), Hor. Ep. 2, 1, 174; id. A. P. 80; 90; Ov. R. Am. 376; Mart. 8, 3, 13: comicus soccus, Plin. 7, 30, 31, § 111; cf.: nec tragoedia socco ingreditur, Quint. 10, 2, 22: risus socci; opp. luctus cothurni, Claud. in Eutr. 1, 299.