Dictionary

(usually with the definite article) A place to do the "necessary" business of urination and defecation: an outhouse or lavatory.

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

Example: Although I wished to think that all was false, it was yet necessary that I, who thus thought, must in some sense exist.

Unavoidable, inevitable.

Example: If it is absolutely necessary to use public computers, you should plan ahead and forward your e-mail to a temporary, disposable account.

Determined, involuntary: acting from compulsion rather than free will.