A prophet appearing reflective after dropping trousers (9)
I believe the answer is:
dungarees
'trousers' is the definition.
'a prophet appearing reflective after dropping' is the wordplay.
'prophet' becomes 'seer' (I've seen this before).
'appearing reflective' says the letters should be written backwards.
'after' means one lot of letters go next to another.
'dropping' becomes 'dung' (**).
'seer' written backwards gives 'rees'.
'a'+'rees'='arees'
'arees' after 'dung' is 'DUNGAREES'.
(Other definitions for dungarees that I've seen before include "Durable overalls" , "Hard-wearing work trousers with a bib" , "Overalls of cotton fabric" , "Work overalls" , "overalls required" .)