Lets gin cocktail sparkle (7)
I believe the answer is:
glisten
'sparkle' is the definition.
(synonyms)
'lets gin cocktail' is the wordplay.
'cocktail' is an anagram indicator.
'lets'+'gin'='letsgin'
'letsgin' with letters rearranged gives 'GLISTEN'.
(Other definitions for glisten that I've seen before include "Shine like something wet" , "Singlet (anag.); tingles (anag.)" , "look bright" , "'Shine, as if wet (7)'" , "Let sing (anag) -- shine" .)