An affair that does have importance (6)
I believe the answer is:
matter
This might be a double definition.
'an affair that does' is the first definition.
'matter' can be an answer for 'an affair' ('matter' can be a synonym of 'affair'). I am not sure about the remainder of the definition.
'importance' is the second definition.
(thesaurus)
'have' is the link.
Can you help me to learn more?
(Other definitions for matter that I've seen before include "Substance as opposed to spirit" , "It occupies space, has substance" , "Affair; be important" , "See 18" , "Physical substance" .)