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Webster 1913 Edition

Noun.

The guard or defense of a castle.

(O. Eng. Law)

A tax or imposition an a dwelling within a certain distance of a castle, for the purpose of maintaining watch and ward in it; castle-ward.

A feudal tenure, obliging the tenant to perform service within the realm, without limitation of time.

Noun.

A feudal tenure, or knight service, which obliged the tenant to perform service within the realm, without limitation of time.

castle-guard ‎(plural castle-guards)

The guard or defence of a castle.
(Britain, law, obsolete) A tax or imposition on a dwelling within a certain distance of a castle, for the purpose of maintaining watch and ward in it; castleward.
A feudal tenure, obliging the tenant to perform service within the realm, without limitation of time.