The cold a companion gets sick of (5)
I believe the answer is:
chill
'the cold' is the definition.
(chill can mean cold)
'a companion gets sick of' is the wordplay.
I cannot quite see how this works, but
'companion' could be 'ch' (Companion of Honour) and 'ch' is present in the answer.
'sick' could be 'ill' (similar in meaning) and 'ill' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for chill that I've seen before include "minor illness" , "nip" , "Make cooler" , "Preserve by cold" , "Refrigerate" .)