The Collaborative International Dictionary of English v.0.48:

Replacement \Re*place"ment\ (-ment), n.
   1. The act of replacing.
      [1913 Webster]

   2. (Crystallog.) The removal of an edge or an angle by one or
      more planes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

replacement
    n 1: the act of furnishing an equivalent person or thing in the
         place of another; "replacing the star will not be easy"
         [syn: replacement, replacing]
    2: someone who takes the place of another person [syn:
       surrogate, alternate, replacement]
    3: an event in which one thing is substituted for another; "the
       replacement of lost blood by a transfusion of donor blood"
       [syn: substitution, permutation, transposition,
       replacement, switch]
    4: a person or thing that takes or can take the place of another
       [syn: substitute, replacement]
    5: filling again by supplying what has been used up [syn:
       refilling, replenishment, replacement, renewal]
    6: a person who follows next in order; "he was President
       Lincoln's successor" [syn: successor, replacement]

Moby Thesaurus II by Grady Ward, 1.0:

102 Moby Thesaurus words for "replacement":
   agency, agent, alternate, alternative, analogy, backup, backup man,
   change, changeling, commutation, comparison, copy, counterfeit,
   delegation, deputation, deputy, deputyship, descendant,
   displacement, double, dummy, equal, equivalent, ersatz, exchange,
   fake, fill-in, ghost, ghostwriter, heir, imitation, improvement,
   inheritor, instauration, locum, locum tenens, makeshift, metaphor,
   metonymy, next best thing, personnel, phony, pinch hitter,
   posterity, power of attorney, proxy, quid pro quo, reactivation,
   reconstitution, reconversion, redintegration, reenactment,
   reestablishment, reformation, rehabilitation, reinstatement,
   reinstation, reinstitution, reinvestiture, reinvestment, relief,
   representation, representative, reserves, restitution, restoration,
   reversion, ringer, second string, secondary, sign, spares,
   stand-in, sub, subrogation, substituent, substitute, substitution,
   succedaneum, successor, supersedence, superseder, superseding,
   supersedure, supersession, supplantation, supplanter, supplanting,
   supplantment, surrogate, switch, symbol, synecdoche, third string,
   tit for tat, token, understudy, utility player, vicar,
   vicariousness, vice-president, vice-regent