NOUN (4)

1. the act of rejecting something;
- Example: "his proposals were met with rejection"

2. the state of being rejected;

3. (medicine) an immunological response that refuses to accept substances or organisms that are recognized as foreign;
- Example: "rejection of the transplanted liver"

4. the speech act of rejecting;

The Collaborative International Dictionary of English v.0.48:

Rejection \Re*jec"tion\ (r?-j?k"sh?n), n. [L. rejectio: cf. F.
   r['e]jection.]
   Act of rejecting, or state of being rejected.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rejection
    n 1: the act of rejecting something; "his proposals were met
         with rejection"
    2: the state of being rejected [ant: acceptance]
    3: (medicine) an immunological response that refuses to accept
       substances or organisms that are recognized as foreign;
       "rejection of the transplanted liver"
    4: the speech act of rejecting

Moby Thesaurus II by Grady Ward, 1.0:

206 Moby Thesaurus words for "rejection":
   Eighteenth Amendment, Prohibition Party, Volstead Act, abnegation,
   agnosticism, agreement to disagree, alienation, apostasy, atheism,
   ban, bar, barring, blackball, blackballing, blockade, booting out,
   boycott, bucking, castaway, castoff, challenge, circumscription,
   cold shoulder, complaint, contention, contraband, contradiction,
   contraposition, contravention, contraversion, counter-culture,
   counteraction, counterworking, crosscurrent, crossing, debarment,
   debarring, declension, declination, declinature, declining,
   deep six, defenestration, demarcation, denial, deprivation,
   detrusion, difference, dim view, disaccord, disagreement,
   disallowance, disappointment, disapprobation, disapproval,
   disbelief, discard, discarding, discharge, disclaimer,
   disclamation, discontent, discontentedness, discontentment,
   discredit, disenchantment, disesteem, disfavor, disgruntlement,
   disillusion, disillusionment, dismissal, disobedience, disparity,
   displeasure, disposal, disrespect, dissatisfaction, dissension,
   dissent, dissentience, dissidence, distaste, diversity,
   dropping out, dumping, ejection, ejectment, elimination, embargo,
   exception, exclusion, expulsion, extrusion, forbiddance,
   forbidden fruit, forbidding, head wind, heresy, holding back,
   impugnation, impugnment, inability to believe, inadmissibility,
   incredulity, index, index expurgatorius,
   index librorum prohibitorum, indignation, infidelity, inhibition,
   injunction, interdict, interdiction, interdictum, jettison,
   junking, kicking downstairs, law, lockout, low estimation,
   low opinion, minimifidianism, minority opinion, misbelief,
   narrowing, nay, negation, negative, negative answer, nix, no,
   no-no, nonacceptance, nonadmission, nonagreement, nonassent,
   nonbelief, noncompliance, nonconcurrence, nonconformity,
   nonconsent, nonobservance, nullifidianism, objection, obtrusion,
   omission, opposing, opposition, opposure, oppugnation, ostracism,
   ouster, ousting, preclusion, prevention, prohibition,
   prohibitory injunction, proscription, protest, rebuff, rebutment,
   rebuttal, recantation, recusance, recusancy, refusal, refuse,
   reject, rejectamenta, relegation, removal, renunciation,
   repression, repudiation, resistance, restriction,
   restrictive covenants, retention, ruling out, scrapping, secession,
   spurning, standing against, statute, sumptuary laws, suppression,
   taboo, the boot, the bounce, throwaway, throwing out, thumbs-down,
   traversal, turndown, unbelief, unbelievingness, undercurrent,
   underground, unhappiness, unwillingness, variance, withdrawal,
   withholding, zoning, zoning laws