Shower, refreshed before trendy thrash (9)
I believe the answer is:
horsewhip
'thrash' is the definition.
(I've seen this before)
'shower refreshed before trendy' is the wordplay.
'refreshed' indicates an anagram.
'before' is a charade indicator (letters next to each other).
'trendy' becomes 'hip' (I've seen this in another clue).
'shower' is an anagram of 'horsew'.
'horsew'+'hip'='HORSEWHIP'
(Other definitions for horsewhip that I've seen before include "scourer of fillies?" , "administer punishment" , "Coachman's accessory" , "punish painfully" , "He worship (anag) - lash" .)