Rotten, putrid (6)
I believe the answer is:
rancid
This clue is a double definition.
'rotten' is the first definition.
(I've seen this in another clue)
'putrid' is the second definition.
(I've seen this before)
(Other definitions for rancid that I've seen before include "Like stale fat or oil" , "Rotten; high" , "Smelly and going bad" , "Unpleasantly stale" , "Smelling or tasting of stale fat" .)