Corrode (4)
I believe the answer is:
rust
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">corrode</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that corrode can be written as rust)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rust that I've seen before include "Reddish coating formed on iron through 11 across" , "Fungal plant disease" , "Reddish-brown coating formed on iron by moisture" , "Reddish-brown coating formed on metal by moisture" , "A fungus; a corrosion" .)