Constituting or existing as a necessary component or ingredient; forming or composing as a necessary part; component; elementary: as, oxygen and hydrogen are the constituent parts of water.Having the power of constituting or appointing, or of electing to public office: as, a constituent body.n. One who or that which constitutes or forms, or establishes or determines.n. That which constitutes or composes as a part, or a necessary part; a formative element or ingredient.n. One who constitutes another his agent; one who empowers another to transact business for him, or appoints another to an office in which the person appointed represents him as his agent.n. One who elects or assists in electing another to a public office; more generally, any inhabitant of the district represented by an elective officer, especially by one elected to a legislative body: so called with reference to such officer.