castle
/ˈkæsəl/ /Brit ˈkɑːsəl/
noun
plural castles
[count] a large building usually with high, thick walls and towers that was built in the past to protect against attack
informal :a large expensive house
a piece in the game of chess that looks like a castle tower :rook
castle in the air
also castle in Spain
a dream, plan, or idea that can never become real - usually plural
US