from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
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.