- essential, indispensable, or requisite: The rotor is a necessary part of the motor.
- happening or existing by necessity: The snow has forced 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.
- something necessary or required for a particular purpose; necessity.
- food, clothing, etc., required by a dependent person and varying with their social or economic position or that of the person upon whom they are dependent.
- a privy or toilet.
- needed to achieve a certain desired effect or result; required
- resulting from necessity; inevitable
- logic
- (of a statement, formula, etc) true under all interpretations or in all possible circumstances
- (of a proposition) determined to be true by its meaning, so that its denial would be self-contradictory
- (of a property) essential, so that without it its subject would not be the entity it is
- (of an inference) always yielding a true conclusion when its premises are true; valid
- (of a condition) entailed by the truth of some statement or the obtaining of some state of affairs
- (in a nonlogical sense) expressing a law of nature, so that if it is in this sense necessary that all As are B, even although it is not contradictory to conceive of an A which is not B, we are licensed to infer that if something were an A it would have to be B
- compelled, as by necessity or law; not free
- the money required for a particular purpose
- to do something that is necessary in a particular situation