Moderate single daughter in urban community (4,4)
I believe the answer is:
tone down
'moderate' is the definition.
(I know that moderate can be written as tone down)
'single daughter in urban community' is the wordplay.
'single' becomes 'one' (synonyms).
'daughter' becomes 'd' (genealogical abbreviation).
'in' means one lot of letters goes inside another.
'urban community' becomes 'town' (a town is an urban area).
'one'+'d'='oned'
'oned' placed inside 'town' is 'TONE DOWN'.
(Other definitions for tone down that I've seen before include "Make less harshly coloured" , "D to C, perhaps?" , "Mute" , "Make less harsh" , "Temper" .)