Pact

Pact (?), n. [L. pactum, fr. paciscere to make a bargain or contract, fr. pacere to settle, or agree upon; cf. pangere to fasten, Gr. ?, Skr. pāca bond, and E. fang: cf. F. pacie. Cf. Peace, Fadge, v.] An agreement; a league; a compact; a covenant. Bacon.

The engagement and pact of society whish goes by the name of the constitution.
Burke.