American uncle turning up in Damascus (3)
I believe the answer is:
sam
'american uncle' is the definition.
(Uncle Sam is a nickname for the USA)
'turning up in damascus' is the wordplay.
'turning up' shows that the letters should be reversed in order.
'in' says the answer is hidden in the clue.
'mas' is hidden in the letters of 'damascus'.
'mas' back-to-front is 'SAM'.
(Other definitions for sam that I've seen before include "Boy" , "Casablanca piano player" , "together once" , "Uncle" .)