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]