The Collaborative International Dictionary of English v.0.48:

Immunity \Im*mu"ni*ty\, n.; pl. Immunities. [L. immunitas, fr.
   immunis free from a public service; pref. im- not + munis
   complaisant, obliging, cf. munus service, duty: cf. F.
   immunit['e]. See Common, and cf. Mean, a.]
   1. Freedom or exemption from any charge, duty, obligation,
      office, tax, imposition, penalty, or service; a particular
      privilege; as, the immunities of the free cities of
      Germany; the immunities of the clergy.
      [1913 Webster]

   2. Freedom; exemption; as, immunity from error.
      [1913 Webster]

   3. The state of being insusceptible to disease, certain
      poisons, etc.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

immunity
    n 1: the state of not being susceptible; "unsusceptibility to
         rust" [syn: unsusceptibility, immunity] [ant:
         susceptibility, susceptibleness]
    2: (medicine) the condition in which an organism can resist
       disease [syn: immunity, resistance]
    3: the quality of being unaffected by something; "immunity to
       criticism"
    4: an act exempting someone; "he was granted immunity from
       prosecution" [syn: exemption, immunity, granting
       immunity]

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "immunity":
   absolution, acquired immunity, active immunity, amnesty, antibody,
   antigen, artificial immunity, assurance, blank check,
   carte blanche, charter, clear sailing, congenital immunity,
   copyright, diplomatic immunity, discharge, dispensation, exception,
   exclusion, exculpation, excuse, exemption, exoneration,
   familial immunity, favor, franchise, freedom, grace, grant,
   harmlessness, immunity theory, immunization, immunization therapy,
   immunochemistry, immunology, immunotherapy, impunity, indemnity,
   indulgence, inherent immunity, inherited immunity, inoculation,
   insusceptibility, invulnerability, legislative immunity, liberty,
   license, natural immunity, nolle prosequi, non prosequitur,
   nonprosecution, nonspecific immunity, nonsusceptibility to disease,
   opsonic immunity, pardon, passive immunity, patch test, patent,
   permission, phagocytic immunity, privilege, protection,
   racial immunity, redemption, release, remission, remission of sin,
   reprieve, resistance, risklessness, safeguard, safeness, safety,
   scratch test, security, serotherapeutics, serotherapy,
   serum therapy, shrift, side-chain theory, sparing, special favor,
   specific immunity, stay, surety, toxin-antitoxin immunity,
   toxin-antitoxin immunization, tuberculin test, unsusceptibility,
   vaccination, vaccine therapy, vaccinotherapy, warrant



Bouvier's Law Dictionary, Revised 6th Ed (1856):

IMMUNITY. An exemption from serving in an office, or performing duties which
the law generally requires other citizens to perform. Vide Dig. lib. 50, t.
6; 1 Chit. Cr. L. 821; 4 Har. & M'Hen. 341.