champerty (n.)

late 14c., champertie, champartie, the illegal act whereby a person not otherwise interested makes a bargain to maintain a litigant in return for a share of the property in dispute if the case succeeds, from Old French champart "portion of produce received by a feudal lord from land held in lease from him" (13c.), from Medieval Latin campipartem, from campi pars "part of the field" (see campus + part (n.)).