Go mouldy (3)
I believe the answer is:
rot
(Other definitions for rot that I've seen before include "Break down, waste away" , "Decay, perish" , "crumble" , "Decay, wither" , "bunk" .)
I believe the answer is:
rot
(Other definitions for rot that I've seen before include "Break down, waste away" , "Decay, perish" , "crumble" , "Decay, wither" , "bunk" .)