facultative

(adjective)

adjective

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

Similar word(s): enabling

4. not compulsory

Similar word(s): optional, elective