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.
  1. (of a proposition) such that a denial of it involves a self-contradiction.
  2. (of an inference or argument) such that its conclusion cannot be false if its supporting premises are true.
  3. (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 nec·es·sar·ies.

Nearby words

  1. necator,
  2. necatoriasis,
  3. necessarian,
  4. necessaries,
  5. necessarily,
  6. necessary condition,
  7. necessary stool,
  8. necessitarian,
  9. necessitarianism,
  10. necessitate

Origin of necessary

1300–50; Middle English necessarie < Latin necessārius unavoidable, inevitable, needful, equivalent to necess(e) (neuter indeclinable adj.) unavoidable, necessary + -ārius -ary

SYNONYMS FOR necessary
1. required, needed. Necessary, essential, indispensable, requisite indicate something vital for the fulfillment of a need. Necessary applies to something without which a condition cannot be fulfilled or to an inevitable consequence of certain events, conditions, etc.: Food is necessary to life. Multiplicity is a necessary result of division. Indispensable applies to something that cannot be done without or removed from the rest of a unitary condition: Food is indispensable to living things. He made himself indispensable as a companion. Something that is essential forms a vitally necessary condition of something: Air is essential to red-blooded animals. It is essential to understand the matter clearly. Requisite applies to what is thought necessary to fill out, complete, or perfect something: She had all the requisite qualifications for a position. 5. requirement, requisite, essential.

ANTONYMS FOR necessary

Related formsnec·es·sar·i·ness, nounqua·si-nec·es·sar·y, adjective

Can be confusednecessary necessitous (see synonym study at the current entry) Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for necessariness



needed to achieve a certain desired effect or result; required
resulting from necessity; inevitablethe necessary consequences of your action
  1. (of a statement, formula, etc) true under all interpretations or in all possible circumstances
  2. (of a proposition) determined to be true by its meaning, so that its denial would be self-contradictory
  3. (of a property) essential, so that without it its subject would not be the entity it is
  4. (of an inference) always yielding a true conclusion when its premises are true; valid
  5. (of a condition) entailed by the truth of some statement or the obtaining of some state of affairsCompare sufficient (def. 2)
philosophy (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
rare compelled, as by necessity or law; not free


the necessary informal the money required for a particular purpose
do the necessary informal to do something that is necessary in a particular situation
See also necessaries

Word Origin for necessary

C14: from Latin necessārius indispensable, from necesse unavoidable

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for necessariness
Online Etymology Dictionary, © 2010 Douglas Harper