Companion with a bad cold (5)
I believe the answer is:
chill
'cold' is the definition.
(chill is a kind of cold)
'companion with a bad' is the wordplay.
'companion' becomes 'ch' (I've seen this in other clues).
'with' is a charade indicator (letters next to each other).
'a bad' becomes 'ill' (I've seen this before).
'ch'+'ill'='CHILL'
(Other definitions for chill that I've seen before include "Slang injunction to relax - it's cold" , "Make cold; relax" , "Unpleasent coldness in the air" , "nip" , "Refrigerate" .)