[1] : The Collaborative International Dictionary of English v.0.48

changeling \change"ling\, a.
   1. taken or left in place of another; changed. "a little
      changeling boy." --shak.
      1913 webster

   2. given to change; inconstant. obs.
      1913 webster

            some are so studiously changeling.    --boyle.
      1913 webster

[2] : The Collaborative International Dictionary of English v.0.48

changeling \change"ling\, n. change + -ling.
   1. one who, or that which, is left or taken in the place of
      another, as a child exchanged by fairies.
      1913 webster

            such, men do changelings call, so changed by
            fairies' theft.                       --spenser.
      1913 webster

            the changeling a substituted writing never known.
                                                  --shak.
      1913 webster

   2. a simpleton; an idiot. --macaulay.
      1913 webster

            changelings and fools of heaven, and thence shut
            out.
      1913 webster

            wildly we roam in discontent about. --dryden.
      1913 webster

   3. one apt to change; a waverer. "fickle changelings."
      --shak.
      1913 webster

[3] : WordNet (r) 2.0

changeling
     n 1: a person of subnormal intelligence syn: idiot, imbecile,
           cretin, moron, half-wit, retard
     2: a child secretly exchanged for another in infancy
see also:
idiot imbecile cretin moron half-wit retard 

[4] : Moby Thesaurus II by Grady Ward, 1.0

58 moby thesaurus words for "changeling":
   agent, alternate, alternative, analogy, backup, change, comparison,
   copy, counterfeit, deputy, double, dummy, elf child, equal,
   equivalent, ersatz, exchange, fake, fill-in, ghost, ghostwriter,
   imitation, locum tenens, makeshift, metaphor, metonymy,
   next best thing, personnel, phony, pinch hitter, proxy, relief,
   replacement, representative, reserves, ringer, second string,
   secondary, sign, spares, stand-in, sub, substituent, substitute,
   substitution, succedaneum, superseder, supplanter, surrogate,
   symbol, synecdoche, third string, token, understudy,
   utility player, vicar, vice-president, vice-regent

Changeling >> C Words
Changeling, definition of term: Changeling
changeling_pag1.html