What is Necessary?

Necessary definition and meaning on Dictionary terms:
being essential, indispensable, or requisite: a necessary part of the motor.
happening or existing by necessity: a necessary change in our plans.
acting or proceeding from compulsion or necessity; not free; involuntary: a necessary agent.
Logic. (of a proposition) such that a denial of it involves a self-contradiction. (of an inference or argument) such that its conclusion cannot be false if its supporting premises are true. (of a condition) such that it must exist if a given event is to occur or a given thing is to exist.Compare sufficient(def 2).

noun, plural necA.esA.sarA.ies.
something necessary or required for a particular purpose; necessity.
necessaries, Law. food, clothing, etc., required by a dependent or incompetent and varying with his or her social or economic position or that of the person upon whom he or she is dependent.

Chiefly New England. a privy or toilet.