Radical former lover, male, housed by elder perhaps (7)
I believe the answer is:
extreme
'radical' is the definition.
(thesaurus)
'former lover male housed by elder perhaps' is the wordplay.
'former lover' becomes 'ex'.
'male' becomes 'm' (common abbreviation).
'housed by' means one lot of letters goes inside another.
'elder perhaps' becomes 'tree' (elder is a kind of tree).
'm' inserted within 'tree' is 'treme'.
'ex'+'treme'='EXTREME'
(Other definitions for extreme that I've seen before include "Of the greatest intensity" , "Severe; radical" , "Acute, maximum" , "sheer" , "Harsh" .)