Case of Clarins tan certain to cover it (8)
I believe the answer is:
instance
'case' is the definition.
(synonyms)
'clarins tan certain to cover it' is the wordplay.
'to cover it' says the answer is hidden in the clue (the answer is covered or hidden by the clue).
'INSTANCE' can be found hidden inside 'clarins tan certain'.
'of' is the link.
(Other definitions for instance that I've seen before include "Occasion" , "Specimen" , "Exemplify" , "A case or example of something" , "Particular example" .)