Possibly an Aberdonian racecourse (5)
I believe the answer is:
ascot
'racecourse' is the definition.
(British racecourse)
'possibly an aberdonian' is the wordplay.
I cannot quite see how this works, but
'an' could be 'a' and 'a' is located in the answer.
'aberdonian' could be 'scot' (I've seen this in another clue) and 'scot' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ascot that I've seen before include "English horse racing venue on coast" , "English town" , "Royal racing venue" , "Where ladies wear new hats" , "Horse-racing venue" .)