• synonyms


[fak-uh l-tey-tiv]
See more synonyms for facultative on Thesaurus.com
  1. conferring a faculty, privilege, permission, or the power of doing or not doing something: a facultative enactment.
  2. left to one's option or choice; optional: The last questions in the examination were facultative.
  3. that may or may not take place; that may or may not assume a specified character.
  4. Biology. having the capacity to live under more than one specific set of environmental conditions, as a plant that can lead either a parasitic or a nonparasitic life or a bacterium that can live with or without air (opposed to obligate).
  5. of or relating to the faculties.
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Origin of facultative

From the New Latin word facultātīvus, dating back to 1810–20. See faculty, -ive
Related formsfac·ul·ta·tive·ly, adverbnon·fac·ul·ta·tive, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words


Examples from the Web for facultative

Historical Examples

  • Thus arobes and facultative anarobes are prototrophic for O.

    The Fundamentals of Bacteriology

    Charles Bradfield Morrey

  • On the whole, perhaps, the "facultative" Referendum is to be preferred to the obligatory.

  • Other important species will be considered as facultative parasites.

    Handbook of Medical Entomology

    William Albert Riley

  • The great majority of milk bacteria are either obligate or facultative aerobes.

  • I have seen this particularly in those cases where facultative divergence also was greater than usual.

British Dictionary definitions for facultative


  1. empowering but not compelling the doing of an act
  2. philosophy that may or may not occur
  3. insurance denoting a form of reinsurance in which the reinsurer has no obligation to accept a particular risk nor the insurer to reinsure, terms and conditions being negotiated for each reinsurance
  4. biology able to exist under more than one set of environmental conditionsa facultative parasite can exist as a parasite or a saprotroph Compare obligate (def. 4)
  5. of or relating to a faculty
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Derived Formsfacultatively, adverb
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

facultative in Medicine


  1. Capable of functioning under varying environmental conditions. Used of certain organisms, such as bacteria that can live with or without oxygen.
  2. Capable of occurring along various pathways or under various conditions.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

facultative in Science


  1. Capable of existing under varying environmental conditions or by assuming various behaviors. Bacteria that are facultative aerobes can live in both aerobic and anaerobic environments. A facultative parasite can live independently of its usual host. Compare obligate.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.