1: the grounds (as violation of a right) that entitle a plaintiff to bring a suit Example: 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 Example: removed the cause of action to the district court
2:
"right of action § 1"
Example: the court, led by Justice Brennan, said Congress intended to provide a private cause of action -- National Law Journal