<p><strong>Adjective</strong></p><ul><li>Essential, indispensable, or requisite: The rotor is a necessary part of the motor.</li><li>Happening or existing by necessity: The snow has forced a necessary change in our plans.</li><li>Acting or proceeding from compulsion or necessity; not free; involuntary: a necessary agent.</li><li>Logic: (of a proposition) such that a denial of it involves a self-contradiction.</li><li>(Of an inference or argument) such that its conclusion cannot be false if its supporting premises are true.</li><li>(Of a condition) such that it must exist if a given event is to occur or a given thing is to exist.</li></ul><p><strong>Noun</strong></p><ul><li>Something necessary or required for a particular purpose; necessity.</li><li>Synonyms: essential, requisite, requirement.</li><li>Necessaries, Law: 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.</li><li>Chiefly New England: a privy or toilet.</li></ul>