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[fak-uh l-tey-tiv] /ˈfæk əlˌteɪ tɪv/
conferring a faculty, privilege, permission, or the power of doing or not doing something:
a facultative enactment.
left to one's option or choice; optional:
The last questions in the examination were facultative.
that may or may not take place; that may or may not assume a specified character.
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).
of or relating to the faculties.
Origin of facultative
From the New Latin word facultātīvus, dating back to 1810-20. See faculty, -ive
Related forms
facultatively, adverb
nonfacultative, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for facultative
Historical Examples
  • Moreover, the extent of the "facultative" divergence attainable by prisms shows a considerable latitude.

    Schweigger on Squint C. Schweigger
  • On the whole, perhaps, the "facultative" Referendum is to be preferred to the obligatory.

  • It is not normally parasitic, however, and hence will be considered with other facultative parasites in Chapter IV.

    Handbook of Medical Entomology William Albert Riley
  • Many are exclusively parasitic or saprophytic, and many are facultative, both conditions of living being possible.

    Disease and Its Causes William Thomas Councilman
  • The minimum O pressure for facultative anarobes is also 0 mm.

    The Fundamentals of Bacteriology Charles Bradfield Morrey
  • It has been shown that if these organisms are grown with arobes or facultative anarobes they thrive at ordinary room temperature.

    The Fundamentals of Bacteriology Charles Bradfield Morrey
  • Thus arobes and facultative anarobes are prototrophic for O.

    The Fundamentals of Bacteriology Charles Bradfield Morrey
  • The existence of anarobic and facultative anarobic bacteria shows the fallacy of such beliefs.

    The Fundamentals of Bacteriology Charles Bradfield Morrey
  • I have seen this particularly in those cases where facultative divergence also was greater than usual.

    Schweigger on Squint C. Schweigger
  • If a parasite cannot exist outside animal tissues, it is an obligatory parasite; if it can, it is a facultative saphrophyte.

British Dictionary definitions for facultative


empowering but not compelling the doing of an act
(philosophy) that may or may not occur
(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
(biology) able to exist under more than one set of environmental conditions: a facultative parasite can exist as a parasite or a saprotroph Compare obligate (sense 4)
of or relating to a faculty
Derived Forms
facultatively, 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
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facultative in Medicine

facultative fac·ul·ta·tive (fāk'əl-tā'tĭv)

  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.

fac'ul·ta'tive·ly adv.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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facultative in Science
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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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