means the apartment or dwelling on the top floor of a building, typically the most luxurious and expensive unit with the best views.

from From Middle English 'pentis,' borrowed from Old French 'apentis' (a lean-to or attached shed), which traces back to Latin 'appendere,' to hang or attach onto. So the word originally meant a humble sloping outbuilding clinging to a larger structure's side — a far cry from luxury. The spelling drifted toward 'penthouse' by folk association with 'house,' and only in the early 20th century did the term climb skyward to mean the grand suite perched on a building's roof.