D defs.my
Entry 3 senses Webster, 1913

Facultative

/făk'-əl-tātˌ-ĭv/ · Fac·ul·ta·tive · IPA /ˈfæ.kəlˌteɪ.tɪv/
01 a. Having relation to the grant or exercise faculty, or authority, privilege, license, or the like hence, optional; as, facultative enactments…
  1. 1.
    Having relation to the grant or exercise faculty, or authority, privilege, license, or the like hence, optional; as, facultative enactments, or those which convey a faculty, or permission; the facultative referendum of Switzerland is one that is optional with the people and is necessary only when demanded by petition; facultative studies; -- opposed to obligatory and compulsory, and sometimes used with to.
  2. 2.
    Of such a character as to admit of existing under various forms or conditions, or of happening or not happening, or the like;(Biol.)
  3. 3.
    Pertaining to a faculty or faculties.(Physiol.)
    “In short, there is no facultative plurality in the mind; it is a single organ of true judgment for all purposes, cognitive or practical.” — J. Martineau.