1. Optional
   "facultative surgery";
   - elective
    
2. (biology) 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. Of or relating to the mental faculties
   "The facultative powers of the human mind allow for complex problem-solving"

See also: enabling, optional

Antonym: obligate

Encyclopedia: Facultative