Writer gulps high tea if blissful (8)
I believe the answer is:
beatific
'blissful' is the definition.
(I've seen this before)
'writer gulps high tea if' is the wordplay.
'writer' becomes 'bic' (Bic is a manufacturer of pens).
'gulps' is an insertion indicator.
'high' indicates an anagram (like drunk).
'tea'+'if'='teaif'
'teaif' anagrammed gives 'eatif'.
'bic' enclosing 'eatif' is 'BEATIFIC'.
(Other definitions for beatific that I've seen before include "supremely happy" , "Showing great happiness, perhaps a smile" , "Joyful" , "Feeling or expressing blissful happiness" , "Angelic, saintly" .)