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.