pent ‧ house /ˈpenthaʊs/ BrE AmE noun [countable]
[ Date: 1300-1400 ; Language: Old French ; Origin: appentis 'structure built against a wall' , probably from Latin appendix ( ⇨ ↑ appendix ); influenced by house ]
a very expensive and comfortable apartment or set of rooms on the top floor of a building:
a £7 million London penthouse
penthouse apartment/flat/suite