Gone off after church with uncle in a dress (9)
I believe the answer is:
cheongsam
'a dress' is the definition.
(type of East Asian dress)
'gone off after church with uncle' is the wordplay.
'off' indicates anagramming the letters.
'after' is a charade indicator (letters next to each other).
'church' becomes 'ch' (abbreviation on maps etc).
'with' means one lot of letters go next to another.
'uncle' becomes 'sam' (Uncle Sam is an example).
'gone' is an anagram of 'eong'.
'eong' after 'ch' is 'cheong'.
'cheong'+'sam'='CHEONGSAM'
'in' is the link.
(Other definitions for cheongsam that I've seen before include "Straight close-fitting dress worn by Chinese women" , "One-piece Chinese dress" , "tight, Chinese dress" , "Chinese habit" , "Tight-fitting Chinese dress with slit skirt" .)