Serving ace to exclude the possibility of one returning at speed, primarily (7)
I believe the answer is:
barista
'possibility of one returning at speed primarily' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'serving ace to exclude' is the wordplay.
'serving' becomes 'ist' (I can't explain this - if you can you should give a lot more credence to this answer).
'ace' becomes 'a' (abbreviation).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'exclude' becomes 'bar' (synonyms).
'ist'+'a'='ista'
'ista' put after 'bar' is 'BARISTA'.
'the' is the link.
Can you help me to learn more?
(Other definitions for barista that I've seen before include "Arabist (anag)" , "coffee-maker" , "person serving drinks" , "coffee-shop employee" , "Coffee expert" .)