Required, essential, whether logically inescapable or needed in order to achieve a desired result or avoid some penalty. / Unavoidable, inevitable.

(chiefly UK, archaic, euphemistic, usually with the definite article) A place to do the "necessary" business of urination and defecation: an outhouse or lavatory. / (obsolete) Necessity.

plural of Necessary

A surname.

plural of necessary

Necessary or indispensable items.

The state or characteristic of being necessary.

(logic) A statement Q in relation to statement P such that P implies Q.

plural of necessary evil

(idiomatic) An unfavorable thing that must be done or accepted, especially because the available alternative courses of action or inaction would be worse.