Stuffier, cold and may be sore (6)
I believe the answer is:
closer
'stuffier' is the definition.
('close' can be a synonym of 'stuffy')
'cold and may be sore' is the wordplay.
'cold' becomes 'cl' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' means one lot of letters go next to another.
'may' is an anagram indicator (I've seen 'might' mean this (I've seen this in other clues)).
'sore' is an anagram of 'oser'.
'cl'+'oser'='CLOSER'
Can you help me to learn more?
(Other definitions for closer that I've seen before include "Stuffier" , "One winds up" , "more precise" , "within a shorter distance" , "Comparatively near" .)