1) An outwork 
fortress; small outwork of a fortification
• (n.) A small outwork of a fortification; a fortilage; -- called also fortelace.
This is a small castle. The term can be used for more than one single fortified building - such a group of towers defended by moats. It may be that it is only documentary evidence that separates this group of buildings to other castles and towers. Licences to crenellate were needed for battlements on these buildings. An example was Horton Castle, n...
small fort or outworks of a fortification
Fort'a·lice noun [ Late Latin fortalitia , or Old French fortelesce . See Fortress .] (Mil.) A small outwork of a fortification; a fortilage; - - called also fortelace . 
small fort or outworks of a fortification
a small fort; an outwork. · a fortress.