facultative

American  

[fak-uhl-tey-tiv] / ˈfæk əlˌteɪ tɪv /

adjective

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.

---

facultative British  

/ ˈfækəltətɪv /

adjective

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 conditions Compare obligate

   a facultative parasite can exist as a parasite or a saprotroph

5. of or relating to a faculty

---

facultative Scientific  

/ făk′əl-tā′tĭv /

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.

2. Compare obligate

---

Other Word Forms

• nonfacultative
  adjective
• facultatively
  adverb

Etymology

Origin of facultative

First recorded in 1820-25; from French facultative (feminine) “conveying or granting a right or power,” from faculté “knowledge, learning, physical or moral capacity,” ultimately from Latin facultāt-, the stem of facultās (originally a doublet of the noun facilitās “ease, ease of performance or completion, facility”) “ability, power, capacity” + -ative adjective suffix; see faculty ( def. ), -ive ( def. )

Example Sentences

As a facultative anaerobic bacterium, it thrives in both oxygen rich and oxygen poor environments, allowing it to multiply inside the oxygen deprived regions commonly found within tumors.

From Science Daily • Jul. 10, 2026

For the first time, scientists have induced facultative parthenogenesis, a form of asexual reproduction, in an animal that usually reproduces sexually.

From Salon • Jul. 28, 2023

Some species, termed facultative parthenogens, alternate between sexual and asexual reproduction.

From Scientific American • Jun. 9, 2023

Animals that exhibit facultative migration can choose to migrate or not.

From Textbooks • Jun. 9, 2022

Three days afterwards single vision, facultative divergence = prism 5°; in the trial of convergence, equalization by means of prism 8°.

From Schweigger on Squint A Monograph by Dr. C. Schweigger by Schweigger, C.