I thought this is helpful...Especially for those writing for first time, those who are new to the Christian Fantasy Realm!
Any Castle not just medieval!
Definition of A Castle
Allure or Wall-walk: passage behind the parapet of a castle wall
Apse: circular or polygonal end of a tower or chapel
Arcading: rows of arches supported on columns, free-standing or attached to a wall (blind arcade)
Arrow Loop: A narrow vertical slit cut into a wall through which arrows could be fired from inside
Ashlar: blocks of smooth, squared stone of any kind
Bailey or Ward: courtyard within the walls of the castle
Ballista: engine resembling a crossbow, used in hurling missiles or large arrows
Barbican: an outwork or forward extension of a castle gateway
Barrel vault: semicircular roof of stone & timber
Bartizan: overhanging corner turret
Bastion: a small tower at the end of a curtain wall or in the middle of the outside wall
Battlement: a narrow wall built along the outer edge of the wall walk to protect soldiers against attack
Belfry: tall, movable wooden tower on wheels, used in sieges
Brattice: (see hoarding)
Buttery: room for the service of beverages
Concentric: having two sets of walls, one inside the other
Crenelation: a notched battlement made up of alternate crenels (openings) and merlons (square sawteeth)
Cross-wall: an internal dividing wall in a great tower
Curtain wall: a castle wall enclosing a courtyard
Cut: assault tower
Corbel: stone bracket projecting from a wall or corner to support a beam
Donjon: the inner stronghold (keep) of a castle
Drawbridge: a wooden bridge leading to a gateway, capable of being raised or lowered
Drum Tower: a round tower built into a wall
Dungeon: the jail, usually found in one of the towers
Enceinte: an enclosing wall, usually exterior, of a fortified place
Embrasure: the low segment of the altering high and low segments of a battlement
Escalade: scaling of a castle wall
Finial: a slender piece of stone used to decorate the tops of the merlons
Forebuilding: a projection in front of a keep or donjon, containing the stairs to the main entrance
Garderobe: latrine
Gate House: the complex of towers, bridges, and barriers built to protect each entrance through a castle or town wall
Hall: principal living quarters of a medieval castle or house
Hoarding: covered wooden gallery affixed to the top of the outside of a tower or curtain to defend the castle
Inner Ward or Inner Bailey: open area in the center of a castle
Keep: the inner stronghold of the castle
Loophole: slit in wall for light, air, or shooting through
Machicolation: a projection in the battlements of a wall with openings through which missiles could be dropped on besiegers
Mangonel: stone:throwing machine worked by torsion, used as a siege weapon against castles
Merlon: part of a battlement, the square "sawtooth" between crenels
Meurtriere: arrow loop, slit in battlement or wall to permit firing of arrows or for observation
Moat: a deep trench usually filled with water that surrounded a castle
Motte: an earthwork mound on which a castle was built
Murder Holes: a section between the main gate and a inner portcullis where arrows, rocks, and hot oil could be dropped from the roof though holes
Oilette: a round opening at the base of a loophole
Oriel or Oriel Window: projecting room on an upper floor, later an upper-floor bay window
Oubliette: a dungeon reached by a trap door
Palisade: a sturdy wooden fence built to enclose a site until a permanent stone wall could be constructed
Parapet: protective wall at the top of a fortification, around the outer side of the wall-walk
Portcullis: vertical sliding wooden grille shod with iron suspended in front of a gateway designed to protect the gate
Postern Gate: a secondary gate or door often located at the rear of the castle.
Putlog Hole: a hole intentionally left in the surface of a wall for insertion of a horizontal pole
Ram: battering ram
Revet: face with a layer of stone, stone slabs etc., for more strength. Some earth mottes were revetted with stone.
Sapping: undermining, as of a castle wall
Screens: wooden partition at the kitchen end of a hall, protecting a passage leading to the buttery, pantry, and kitchen
Solar: originally a room above ground level, but commonly applied to the great chamber or a private sitting room off the great hall
Springald: war engine of the catapult type, employing tension
Trebuchet: war engine developed in the Middle Ages employing counterpoise
Turning Bridge: a drawbridge that pivoted in the middle
Turret: a small tower rising above and resting on one of the main towers, usually used as a look out point
Wall Walk: the area along the tops of the walls from which soldiers could defend the castle
Ward: courtyard or bailey