Harm barrier with endless rages (6)
I believe the answer is:
damage
'harm' is the definition.
('damage' can be a synonym of 'harm')
'barrier with endless rages' is the wordplay.
'barrier' becomes 'dam' (dam is a kind of barrier).
'with' means one lot of letters go next to another.
'endless' indicates the central letters.
The central letters of 'rages' are 'age'.
'dam'+'age'='DAMAGE'
(Other definitions for damage that I've seen before include "Harm, injury" , "Impairment, injury" , "vandalism?" , "'Deface, impair (6)'" , "Cost (slang)" .)