Conceivably isn't acne in this case (8)
I believe the answer is:
instance
'this case' is the definition.
(I know this)
'conceivably isn't acne' is the wordplay.
'conceivably' indicates anagramming the letters (can conceive it with letters in different order).
'isnt'+'acne'='isntacne'
'isntacne' with letters rearranged gives 'INSTANCE'.
'in' is the link.
(Other definitions for instance that I've seen before include "Particular example" , "Example or single occurrence of something" , "Occasion" , "Case in point" , "Exemplify" .)