The most common and most likely answer to this crossword clue is the 7 letter word CHATEAU
I've seen this crossword clue in Financial Times
C
H
A
T
E
A
U
More clues leading to the result CHATEAU
- Cat seen by water in French country house
- Bird taking water in French country house
- Some of public hate Audi estate
- Cat taking water in French country house
- Stately home abroad serving up two teas and ultimate in tiramisu
- Companion with cake failing to open large country house
- Two forms of Assam, say, served by upper-class Frenchhouse
- Gas and water in French country house
- Double quantities of drink universal in country house
- Can’t stand around outside Nancy’s posh residence
Buddy explains!

The straight part
We know that "castle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case castle = chateau.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CHATEAU mean?
CHATEAU noun- A French castle, fortress, manor house, or large country house.
- Any stately residence imitating a distinctively French castle.
- An estate where wine is produced and often bottled, especially in Bordeaux.