Damages new marsh (5)
I believe the answer is:
harms
'damages' is the definition.
('harm' can be a synonym of 'damage')
'new marsh' is the wordplay.
'new' indicates anagramming the letters.
'marsh' anagrammed gives 'HARMS'.
(Other definitions for harms that I've seen before include "Injures, damages" , "Hurts, damages" , "Wounds" .)