Stiff - but relaxing (9)

I believe the answer is:

unbending

I believe this is a double definition.

'stiff' is the first definition.
(thesaurus)

'relaxing' is the second definition.
(unbending is a kind of relaxing)

'but' is the link.

(Another definition for unbending that I've seen is " Rigid".)

I've seen this clue in The Globe and Mail.

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