morally or legally constraining or binding

anything indispensable, A necessity or prerequisite; something required or obligatory, That which requires the doing of something; an authoritative or imperative command; an essential condition; claim

required by rule, Obligatory, necessary for relief or supply, verb_ Simple past tense and past participle of require

consider obligatory; request and expect, make someone do something, require as useful, just, or proper, transitive To demand; to insist upon having; to claim as by right and authority; to exact, To demand or exact as indispensable; to need, To have as a requisite or necessity; need or depend on