Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
Different from the ordinary prison in being more severe as a place of punishment. Like the Roman inner prison (Acts 16:24), it consisted of a deep cell or cistern (Jer. 38:6). To be shut up in, a punishment common in Egypt (Gen. 39:20, 40:3, 41:10, 42:19). It is not mentioned, however, in the law of Moses as a mode of punishment. Under the later kings imprisonment was frequently used as a punishment (2 Chr. 16:10; Jer. 20:2, 32:2, 33:1, 37:15), and it was customary after the Exile (Mt. 11:2; Lk. 3:20; Acts 5:18, 21; Mt. 18:30).