The Collaborative International Dictionary of English v.0.48:

Infection \In*fec"tion\, n. [Cf. F. infection, L. infectio a
   dyeing.]
   [1913 Webster]
   1. The act or process of infecting.
      [1913 Webster]

            There was a strict order against coming to those
            pits, and that was only to prevent infection. --De
                                                  Foe.
      [1913 Webster]

   2. That which infects, or causes the communicated disease;
      any effluvium, miasm, or pestilential matter by which an
      infectious disease is caused.
      [1913 Webster]

            And that which was still worse, they that did thus
            break out spread the infection further by their
            wandering about with the distemper upon them. --De
                                                  Foe.
      [1913 Webster]

   3. The state of being infected; the condition of suffering
      from an infectious disease; contamination by morbific
      particles; the result of infecting influence; a prevailing
      disease; epidemic.
      [1913 Webster]

            The danger was really very great, the infection
            being so very violent in London.      --De Foe.
      [1913 Webster]

   4. That which taints or corrupts morally; as, the infection
      of vicious principles.
      [1913 Webster]

            It was her chance to light
            Amidst the gross infections of those times.
                                                  --Daniel.
      [1913 Webster]

   5. (Law) Contamination by illegality, as in cases of
      contraband goods; implication.
      [1913 Webster]

   6. Sympathetic communication of like qualities or emotions;
      influence.
      [1913 Webster]

            Through all her train the soft infection ran.
                                                  --Pope.
      [1913 Webster]

            Mankind are gay or serious by infection. --Rambler.

   7. A localized area of tissue which is inflamed by growth of
      microorganisms; as, he has an infection in his finger.
      [PJC]

   Syn: Infection, Contagion.

   Usage: Infection is often used in a definite and limited
          sense of the transmission of affections without direct
          contact of individuals or immediate application or
          introduction of the morbific agent, in
          contradistinction to contagion, which then implies
          transmission by direct contact. --Quain. See
          Contagious.
          [1913 Webster]

WordNet (r) 3.0 (2006):

infection
    n 1: the pathological state resulting from the invasion of the
         body by pathogenic microorganisms
    2: (phonetics) the alteration of a speech sound under the
       influence of a neighboring sound
    3: (medicine) the invasion of the body by pathogenic
       microorganisms and their multiplication which can lead to
       tissue damage and disease
    4: an incident in which an infectious disease is transmitted
       [syn: infection, contagion, transmission]
    5: the communication of an attitude or emotional state among a
       number of people; "a contagion of mirth"; "the infection of
       his enthusiasm for poetry" [syn: contagion, infection]
    6: moral corruption or contamination; "ambitious men are led
       astray by an infection that is almost unavoidable"
    7: (international law) illegality that taints or contaminates a
       ship or cargo rendering it liable to seizure

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "infection":
   abomination, adulteration, aerial infection, afflatus,
   airborne infection, animating spirit, animation, animus, atrocity,
   bad, bane, befouling, befoulment, besmirchment, blight, carrier,
   communicability, contagion, contagiousness, contamination,
   corruption, crying evil, cryptogenic infection, damage, defilement,
   despoliation, destruction, detriment, direct infection, dirtying,
   divine afflatus, droplet infection, dust infection, enlivenment,
   envenoming, epidemiology, evil, exhilaration, festering, fire,
   firing, fouling, genius, grievance, hand infection, harm, havoc,
   hurt, ill, indirect infection, infectiousness, infusion, injury,
   inspiration, mischief, misuse, moving spirit, outrage, perversion,
   phytogenic infection, poison, poisoning, pollution,
   primary infection, prostitution, pyogenic infection,
   ritual uncleanness, secondary infection, soiling,
   subclinical infection, suppuration, taint, the worst, toxin,
   vector, venom, vexation, virus, vitiation, waterborne infection,
   woe, wrong, zoogenic infection