Gossip about old medium? It's not important (2,6)
I believe the answer is:
no matter
'it's not important' is the definition.
(I've seen this before)
'gossip about old medium?' is the wordplay.
'gossip' becomes 'natter' ('natter' can be a synonym of 'gossip'**).
'about' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'medium?' becomes 'm' (as in UK clothing sizes).
'o'+'m'='om'
'natter' placed around 'om' is 'NO MATTER'.
(Other definitions for no matter that I've seen before include "What's in a vacuum" , "Don't mind" , "Irrespective of" , "Regardless of" , "That is trivial" .)