counterplea
    n 1: a plaintiff's reply to a defendant's plea

COUNTERPLEA, pleading. When a tenant in any real action, tenant by the 
curtesy, or tenant in dower, in his answer and plea, vouches any one to 
warrant his title, or prays in aid another who has a larger estate, as of 
the remainder-man or reversioner or when a stranger to the action comes and 
prays to be received to save his estate; then that which the defendant 
alleges against it, why it should not be admitted, is called a counterplea. 
T. de la Ley; Doct. Placit. 300 Com. Dig. h.t.; Dane's Ab. Index, h.t.