The most common and most likely answer to this crossword clue is the 7 letter word CITADEL
I've seen this crossword clue in Independent
C
I
T
A
D
E
L
More clues leading to the result CITADEL
- Fortress initially constructed with ornate detail
- Kremlin directed a jerk in the wrong direction
- Fortress — it's captured by rogue with the Spanish
- Solicit a delegate guarding stronghold
- Elaborate detail under roof of Chinese fortress
- Channel Islands’ reservists take on key fortress
- Keep coming over chilled at Iceland stores
- Castle, possibly getting laid etc, erupted
- Peculiar dialect used in a Salvation Army meeting hall
- Quote line about a Duke in fortress
Buddy explains!

The straight part
We know that "Keep" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case keep = citadel.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 CITADEL mean?
CITADEL noun- A strong fortress that sits high above a city.
- (sometimes figurative) A stronghold or fortified place.
- An armoured portion of a warship, housing important equipment.
- A Salvation Army meeting place.