facultative

/ˌfækəlˈteɪdɪv/

Definitions of facultative

1. adjective

   of or relating to the mental faculties
2. adjective

   granting a privilege or permission or power to do or not do something
   “a facultative enactment”

   synonyms:

   enabling

   providing legal power or sanction
3. adjective

   able to exist under more than one set of conditions
   “a facultative parasite can exist as a parasite or a saprophyte”

   antonyms:

   obligate

   restricted to a particular condition of life
4. adjective

   not compulsory
   “facultative courses in the sciences”

   synonyms:

   optional

   possible but not necessary; left to personal choice