Definition: Officium is the Latin word for duty. The Romans had many types of officia (pl. of officium). Officium amicitiae was the obligation of friendship. Officium virile referred to duties for men from which women were excluded, like representing another at trial or acting as guardian.
Officium was also applied to public law as the official duties of a magistrate or provincial official.
"De officio" is the title of works about or "on the duties", "ex officio" refers to something by virtue of one's duties.
Source: Encyclopedic Dictionary of Roman Law, by Adolf Berger Transactions of the American Philosophical Society © 1953 American Philosophical Society
