Here's a breakdown of the etymology:
* Latin: *castellum* - a fortified place, small castle
* Old French: *chastel* - castle, fortress
* Middle French: *chastel* - castle, manor house, mansion
* Modern French: *château* - castle, mansion, country house
Over time, the meaning of the word "chateau" evolved. While originally referring to fortified castles, it came to encompass larger, more luxurious country houses, often associated with nobility or wealth.
Therefore, "chateau" essentially means "castle" in its most direct sense but now often refers to a grand country house or estate.