Main son ran manor (7)
I believe the answer is:
mansion
'manor' is the definition.
(thesaurus)
'main son ran' is the wordplay.
'ran' indicates an anagram (letters have run around).
'main'+'son'='mainson'
'mainson' anagrammed gives 'MANSION'.
(Other definitions for mansion that I've seen before include "Imposing house" , "Handsome house as for Lord Mayor" , "Opulent house" , "Manor house" , "Large building" .)