Stay within a stronghold (4)

I believe the answer is:

keep

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This clue could be a double definition.

'stay within' is the first definition.
'keep' can be an answer for 'stay' (keeping is a kind of staying). I'm unsure of the 'within' bit.

'a stronghold' is the second definition.
(keep is a kind of stronghold)

Can you help me to learn more?

(Other definitions for keep that I've seen before include "Retain in old castle tower?" , "strong position" , "Stock" , "Retain; strong tower" , "Subsistence" .)

I've seen this clue in the Evening Standard.

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