Chaps in A & E returned for medical treatment (5)
I believe the answer is:
enema
'medical treatment' is the definition.
(I know this)
'chaps in a e returned' is the wordplay.
'chaps' becomes 'men' (chap means a man).
'in' means one lot of letters goes inside another.
'returned' is a reversal indicator.
'a'+'e'='ae'
'men' going within 'ae' is 'amene'.
'amene' back-to-front is 'ENEMA'.
'for' acts as a link.
(Other definitions for enema that I've seen before include "Fluid injected rectally" , "Bowel evacuator" , "fundamental procedure?" , "Suppository" , "Liquid injection given as a laxative" .)