Extra part of room, or extension (4)

I believe the answer is:

'extra' is the definition.
(both can mean additional)

'part of room or extension' is the wordplay.
'part of' indicates a hidden word.
'MORE' is hidden within 'room or extension'.

(Other definitions for more that I've seen before include "Writer" , "A greater amount" , "What Oliver wanted" , "Extra (for Sir Thomas?)" , "victim of Henry" .)

I've seen this clue in The Times.

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