God holding new Sunday mass? (7)
I believe the answer is:
density
'mass?' is the definition.
(thesaurus)
'god holding new sunday' is the wordplay.
'god' becomes 'deity' ('deity' can be a synonym of 'god'**).
'holding' means one lot of letters goes inside another.
'new' becomes 'n'.
'sunday' becomes 's'.
'n'+'s'='ns'
'deity' placed around 'ns' is 'DENSITY'.
(Other definitions for density that I've seen before include "showing obtuseness" , "can be relative" , "Mass per volume" , "Number of items in a given area" , "Degree of compactness" .)