The Collaborative International Dictionary of English v.0.48:

Lawsuit \Law"suit`\, n.
   An action at law; a suit in equity or admiralty; any legal
   proceeding before a court for the enforcement of a claim.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lawsuit
    n 1: a comprehensive term for any proceeding in a court of law
         whereby an individual seeks a legal remedy; "the family
         brought suit against the landlord" [syn: lawsuit, suit,
         case, cause, causa]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "lawsuit":
   accusal, accusation, accusing, action, allegation, allegement,
   arraignment, bill of particulars, blame, bringing of charges,
   bringing to book, case, cause, charge, complaint, count, delation,
   denouncement, denunciation, impeachment, implication, imputation,
   indictment, information, innuendo, insinuation, laying of charges,
   plaint, prosecution, reproach, suit, taxing, true bill,
   unspoken accusation, veiled accusation