Number husband redeveloped, under 500 (7)
I believe the answer is:
hundred
'number' is the definition.
(hundred is a kind of number)
'husband redeveloped under 500' is the wordplay.
'husband' becomes 'h'.
'redeveloped' is an anagram indicator.
'500' becomes 'd' ('d' can be a synonym of '500').
'under' anagrammed gives 'undre'.
'h'+'undre'+'d'='HUNDRED'
(Other definitions for hundred that I've seen before include "entirely associated with 27 [PERCENT]" , "so many others" , "Old division of a county" , "part of Chilterns maybe" , "Ten squared" .)