Lewis & Short

ergastŭlum, i, n. [ἐργάζομαι], a workhouse for offenders (slaves, debtors, etc.), a house of correction, penitentiary.

  1. I. Prop., Col. 1, 6, 3; 1, 8, 16; Cic. Clu. 7, 21; id. Rab. Perd. 7, 20; Liv. 2, 23; 7, 4; Suet. Aug. 32; id. Tib. 8 al.; Vulg. Exod. 6, 6 al.
  2. II. Transf., in plur., ergastula, ōrum, n. (like stabula, servitia, mancipia, etc.), the inmates of a workhouse, penitentiary convicts, * Caes. B. C. 3, 22, 2; Brutus ap. Cic. Fam. 11, 13, 2; Plin. 18, 6, 7, § 36; Flor. 4, 8, 1; Juv. 14, 24 al.
    In the masc. sing.: ergastŭlus = ergastularius, a foreman in a workhouse, Lucil. ap. Non. 447, 7 sq.