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]