In your mouth, it's tender fruitless sweet spot (7)

I believe the answer is:

gumboil

'in your mouth it's tender' is the definition.
(type of mouth ulcer)

'fruitless sweet spot' is the wordplay.
'fruitless sweet' becomes 'gum'.
'spot' becomes 'boil' (**).
'gum'+'boil'='GUMBOIL'

(Other definitions for gumboil that I've seen before include "Swelling in the mouth" , "Small abscess of the mouth" .)

I've seen this clue in The Guardian.

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