OBLIGATORY

obligatory

(adjective) morally or legally constraining or binding; “attendance is obligatory”; “an obligatory contribution”

obligatory

(adjective) required by obligation or compulsion or convention; “he made all the obligatory apologies”

Source: WordNet® 3.1

Etymology

Adjective

obligatory (comparative more obligatory, superlative most obligatory)

Imposing obligation, legally or morally; binding.

Requiring a matter or obligation.

Synonyms

• bounden

• mandatory

Antonyms

• optional

Source: Wiktionary

Ob"li*ga*to*ry, a. Etym: [L. obligatorius: cf.F. obligatoire.]

Definition: Binding in law or conscience; imposing duty or obligation; requiring performance or forbearance of some act; -- often followed by on or upon; as, obedience is obligatory on a soldier. As long as the law is obligatory, so long our obedience is due. Jer. Taylor.

Source: Webster’s Unabridged Dictionary 1913 Edition