E·lect·ive a.
 1. Exerting the power of choice; selecting; as, an elective act.
 2. Pertaining to, or consisting in, choice, or right of choosing; electoral.
    The independent use of their elective franchise.   --Bancroft.
 3. Bestowed or passing by election; as, an elective office.
    Kings of Rome were at first elective; . . . for such are the conditions of an elective kingdom.   --Dryden.
 4. Dependent on choice; that can be refused; as, an elective college course.  Opposite of required or mandatory.
 Elective affinity or Elective attraction Chem., a tendency to unite with certain things; chemism.