Stuffier cold may be the sore type (6)
I believe the answer is:
closer
'stuffier' is the definition.
('close' can be a synonym of 'stuffy')
'cold may be the sore type' is the wordplay.
'cold may be' becomes 'cl' (I can't explain this - if you can you should give a lot more credence to this answer).
'type' indicates an anagram.
'sore' anagrammed gives 'oser'.
'cl'+'oser'='CLOSER'
Can you help me to learn more?
(Other definitions for closer that I've seen before include "Stuffier" , "Comparatively near" , "within a shorter distance" , "Nearer in time or space" , "denser" .)