The Collaborative International Dictionary of English v.0.48:

Parasitism \Par"a*si`tism\ (p[a^]r"[.a]*s[imac]`t[i^]z'm; 277),
   n. [Cf. F. parasitisme.]
   [1913 Webster]
   1. The state or behavior of a parasite; the act of a
      parasite. "Court parasitism." --Milton.
      [1913 Webster]

   2. (Bot. & Zool.) The state of being parasitic.
      [1913 Webster]

WordNet (r) 3.0 (2006):

parasitism
    n 1: the relation between two different kinds of organisms in
         which one receives benefits from the other by causing
         damage to it (usually not fatal damage)

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "parasitism":
   accompaniment, accordance, agreement, alliance, apple-polishing,
   ass-kissing, association, backscratching, bootlicking,
   brown-nosing, cahoots, co-working, coaction, coincidence,
   collaboration, collectivity, collusion, combination,
   combined effort, commensality, concert, concerted action,
   concomitance, concordance, concourse, concurrence, confluence,
   conjunction, consilience, conspiracy, cooperation, correspondence,
   cringing, ecology, ecosystem, fawnery, fawning, flunkyism,
   footlicking, groveling, handshaking, ingratiation, insinuation,
   junction, mealymouthedness, obeisance, obsequiousness, prostration,
   saprophytism, simultaneity, sponging, sycophancy, symbiosis,
   symbiotics, synchronism, synergy, timeserving, toadeating,
   toadying, toadyism, truckling, tufthunting, union, united action