Definition 1: the grounds (as violation of a right) that entitle a plaintiff to bring a suit <an amended pleading reiterating a cause of action for lost profits J. H. Friedenthal et al.> also : the part of a suit brought on those grounds <removed the cause of action to the district court> 2: See also right of action <the court, led by Justice Brennan, said Congress intended to provide a private cause of action National Law Journal>