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]

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "elective":
   academic specialty, adoptive, alternative, appointive, arbitrary,
   area, autonomous, choosing, choosy, classical education,
   constituent, core curriculum, course, course of study, curriculum,
   discipline, discretional, discretionary, discriminating,
   disjunctive, eclectic, electoral, field, free, free will,
   general education, general studies, gratuitous, humanities,
   independent, liberal arts, major, minor, nonmandatory, offered,
   optional, particular, proffered, proseminar, quadrivium,
   refresher course, scientific education, selecting, selective,
   self-acting, self-active, self-determined, self-determining,
   seminar, specialty, spontaneous, study, subdiscipline, subject,
   technical education, trivium, unasked, unbesought, unbidden,
   uncalled-for, uncoerced, uncompelled, unforced, uninfluenced,
   uninvited, unpressured, unprompted, unrequested, unrequired,
   unsolicited, unsought, volitional, voluntary, volunteer, willful