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 know nothing about this answer so I can't tell whether it can be defined by this definition.
'serving ace to exclude' is the wordplay.
'serving' becomes 'ist' (I can't explain this - if you can you should believe this answer much more).
'ace' becomes 'a' (abbreviation).
'to' says to put letters next to each other (I've seen this in other clues).
'exclude' becomes 'bar' (synonyms).
'ist'+'a'='ista'
'ista' after 'bar' is 'BARISTA'.
'the' acts as a 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" .)