facultative (adj.)

  1. of or relating to the mental faculties

  2. able to exist under more than one set of conditions; a facultative parasite can exist as a parasite or a saprophyte'

  3. granting a privilege or permission or power to do or not do something; a facultative enactment'

  4. not compulsory; facultative courses in the sciences'

The dictionary is based on the WordNet Electronic Lexical Database.
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