Rotten, bad (3)
I believe the answer is:
off
I believe this is a double definition.
'rotten' is the first definition.
(rotten food is 'off')
'bad' is the second definition.
(eg meat that's gone off is bad)
(Other definitions for off that I've seen before include "Away, at a distance" , "Gone - bad" , "Rancid or not in operation" , "Unsatisfactory" , "Away, or beginning to decay" .)