Grotto beside reservation (6)

I believe the answer is:

caveat

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'reservation' is the definition.
(I've seen this before)

'grotto beside' is the wordplay.
'grotto' becomes 'cave' (I've seen this in another clue).
'beside' becomes 'at' (I am not sure about this - if you are sure you should believe this answer much more).
'cave'+'at'='CAVEAT'

Can you help me to learn more?

(Other definitions for caveat that I've seen before include "Caution - qualification" , "Warning (of conditions)" , "'Warning, proviso (6)'" , "Warning, eg to buyer" , "A warning against certain acts" .)

I've seen this clue in The Irish Times.

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