Then from main exterior (4)

I believe the answer is:

'then' is the definition.
(thesaurus)

'from main exterior' is the wordplay.
'from' indicates a hidden word.
'NEXT' is hidden within 'main exterior'.

(Other definitions for next that I've seen before include "Following in sequence" , "shop" , "Neighbour lives in the house . . . . door" , "First in line" , "The second cherry stone on the plate" .)

I've seen this clue in The Mirror.

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