Foul gas given off by knitted cardigans (6)
I believe the answer is:
rancid
'foul' is the definition.
(I've seen this in another clue)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for rancid that I've seen before include "Tasting or smelling sour, butter say" , "Rank, high" , "Rotten; high" , "No longer fresh" , "Sour, rotting" .)