Drunk certain to miss one drink? (6)
I believe the answer is:
nectar
'drink?' is the definition.
(nectar is a kind of drink)
'drunk certain to miss one' is the wordplay.
'drunk' is an anagram indicator.
'to miss' is a deletion indicator.
'one' becomes 'i' (Roman numeral).
'certain' with 'i' taken away is 'certan'.
'certan' anagrammed gives 'NECTAR'.
(Other definitions for nectar that I've seen before include "Bees drink it" , "sweet stuff" , "Honey of flowers - drink of the gods" , "sweet thing" , "Sweet, delicious, drink" .)