Eat away, rust (7)
I believe the answer is:
corrode
I believe this is a double definition.
'eat away' is the first definition.
(I've seen this before)
'rust' is the second definition.
(I know that rust can be written as corrode)
(Other definitions for corrode that I've seen before include "Gradually eat away" , "Chemically weaken" , "Eg, to rust" , "Gradually weaken (metal)" , "Growth in hazel buds" .)