a large building formerly occupied by a ruler and fortified against attack
"The guide led us through the ancient castle, pointing out the thick stone walls that once protected the king from invaders."
A large building that is fortified and contains many defences; in previous ages often inhabited by a nobleman or king.
"The tourists marveled at the ancient castle, its towering walls and moat serving as formidable defenses against invaders long ago."
In plain English: A castle is a large, strong building with high walls and towers that kings and queens used to live in long ago.
"The tourists took photos in front of the ancient castle perched on the hill."
Usage: Use the word castle to describe a large, fortified residence historically occupied by royalty or nobility. It refers specifically to grand structures with defensive walls rather than modern mansions or generic houses.
move the king two squares toward a rook and in the same move the rook to the square next past the king
"After developing his pieces for hours, he finally played the long-awaited castle to secure the safety of his monarch."
To house or keep in a castle.
"After being captured in battle, the king was taken to the dungeon of a nearby castle where he remained for several months before his release."
In plain English: To castle means to move your king and rook together in chess to get out of check.
"The storm began to castle over the hills, forming thick clouds that looked like fortresses."
Usage: There is no common everyday usage where "castle" functions as a verb to mean housing someone; this construction is archaic and rarely seen outside of historical fiction. In modern English, you should use synonyms like "imprison," "house," or "shelter" depending on the intended meaning.
A surname, from common nouns referring to someone who lived in or worked in a castle
"The new owner of the vineyard turned out to be Mr. Castle, whose ancestors had been granted the land centuries ago for their service at the nearby fortress."
The word castle entered English from Old French in the late 10th century, originally referring to a small camp or fort before coming to mean the large fortified structures known today. It is derived from the Latin diminutive castellum, which itself comes from castrum, meaning "camp" or "stronghold."