A term used in the Roman law to denote a forced or compulsory service exacted by the government for public purposes; as a forced rendition of labor or goods for the public service. See Dig. 50. 4. 18, 4. In maritime law. A forced service, (onus,) imposed on a vessel for public purposes; an impressment of a vessel. Locc. de Jure Mar. lib. 1, c. 5,