facultative: Meaning and Definition of

fac•ul•ta•tive

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. 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 pertaining to the faculties.