The Collaborative International Dictionary of English v.0.48:

Litigate \Lit"i*gate\, v. t. [imp. & p. p. Litigated; p. pr. &
   vb. n. Litigating.] [See Litigation.]
   To make the subject of a lawsuit; to contest in law; to
   prosecute or defend by pleadings, exhibition of evidence, and
   judicial debate in a court; as, to litigate a cause.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Litigate \Lit"i*gate\, v. i.
   To carry on a suit by judicial process.
   [1913 Webster]

WordNet (r) 3.0 (2006):

litigate
    v 1: engage in legal proceedings
    2: institute legal proceedings against; file a suit against; "He
       was warned that the district attorney would process him";
       "She actioned the company for discrimination" [syn: action,
       sue, litigate, process]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "litigate":
   bring action against, bring into court, bring suit,
   bring to justice, bring to trial, drag into court,
   go into litigation, go to law, implead, law, prosecute,
   prosecute at law, put in suit, put on trial, seek in law,
   seek justice, sue, take to court