The Collaborative International Dictionary of English v.0.48:

Elective \E*lect"ive\, n.
   In an American college, an optional study or course of study;
   a course that is not required. [Colloq.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Elective \E*lect"ive\, a. [Cf. F. ['e]lectif.]
   1. Exerting the power of choice; selecting; as, an elective
      act.
      [1913 Webster]

   2. Pertaining to, or consisting in, choice, or right of
      choosing; electoral.
      [1913 Webster]

            The independent use of their elective franchise.
                                                  --Bancroft.
      [1913 Webster]

   3. Bestowed or passing by election; as, an elective office.
      [1913 Webster]

            Kings of Rome were at first elective; . . . for such
            are the conditions of an elective kingdom. --Dryden.
      [1913 Webster]

   4. Dependent on choice; that can be refused; as, an elective
      college course. Opposite of required or mandatory.
      [1913 Webster +PJC]

   Elective affinity or Elective attraction (Chem.), a
      tendency to unite with certain things; chemism.
      [1913 Webster]

WordNet (r) 3.0 (2006):

elective
    adj 1: subject to popular election; "elective official" [syn:
           elective, elected] [ant: appointed, appointive]
    2: not compulsory; "elective surgery"; "an elective course of
       study"
    n 1: a course that the student can select from among
         alternatives [syn: elective course, elective]