Really very indifferent (2-2)
I believe the answer is:
so-so
'indifferent' is the definition.
(I know that indifferent can be written as so-so)
'really very' is the wordplay.
'really' becomes 'so' (both can mean 'extremely').
'very' becomes 'so' (both can mean 'extremely').
'so'+'so'='SO-SO'
(Other definitions for so-so that I've seen before include "Rather middling" , "Only moderately good in repetitive way" , "Indifferently good" , "Of middling quality" , "just about adequate" .)