The Collaborative International Dictionary of English v.0.48:

decontaminate \de`con*tam"i*nate\
   (d[-e]`k[u^]n*t[a^]m"[i^]*n[=a]t), v. t.
   To remove contamination or contaminants from, by a cleansing
   process; -- usually used of radioactive, infectious, or toxic
   materials; as, to decontaminate clothing worn by persons with
   infective disease; decontaminate an area of PCB's after
   explosion of a transformer.
   [PJC]

WordNet (r) 3.0 (2006):

decontaminate
    v 1: rid of contamination; "The soil around the housing
         development had to be decontaminated by the city" [ant:
         contaminate]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "decontaminate":
   absolve, acquit, amnesty, antisepticize, autoclave, boil,
   chlorinate, clear, delouse, destigmatize, discharge, disinfect,
   dismiss, dispense from, exculpate, excuse, exempt, exempt from,
   exonerate, forgive, free, fumigate, give absolution,
   grant amnesty to, grant immunity, grant remission, hygienize,
   justify, let go, let off, nonpros, pardon, pasteurize, purge,
   quash the charge, release, remit, sanitate, sanitize, set free,
   shrive, sterilize, vindicate, whitewash, withdraw the charge