adjective. Of the nature of an obligation; compulsory.

adjective. Required as part of a routine course of action or cultural expectation; predictable.

adjective. Obligate.

Imposing obligation; binding in law or conscience; imposing duty; requiring performance of or forbearance from some act: followed by on before the person, formerly by to.

adjective. Binding in law or conscience; imposing duty or obligation; requiring performance or forbearance of some act; -- often followed by on or upon.

adjective. Imposing obligation, morally or legally; binding: an obligatory promise.

adjective. Requiring a matter or obligation.

adjective. required by obligation or compulsion or convention

adjective. morally or legally constraining or binding