It's unimportant gossip about old maiden (2,6)
I believe the answer is:
no matter
'it's unimportant' is the definition.
(I've seen this before)
'gossip about old maiden' is the wordplay.
'gossip' becomes 'natter' ('natter' can be a synonym of 'gossip'**).
'about' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'maiden' becomes 'm' (cricket abbreviation).
'o'+'m'='om'
'natter' enclosing 'om' is 'NO MATTER'.
(Other definitions for no matter that I've seen before include "What's in a vacuum" , "Regardless of" , "pure energy?" , "Irrespective of" , "Forget it!" .)