The definition of a penthouse is an apartment, house or other accommodation that is located on the roof of a building.(noun)
An example of a penthouse is the expensive, exclusive, luxurious apartment on the 25th floor of a 25-story building that provides its occupant with an expansive view of the city.
See penthouse in Webster's New World College Dictionary
Origin: altered (infl. by house) < pentice < ME pentis, penthouse < MFr apentis < ML appenticium < LL appendicium, lit., an appendage < L appendere: see append
See penthouse in American Heritage Dictionary 4
Origin: Alteration of Middle English pentis, pentace, a shed attached to a wall of a building
Origin: , from Anglo-Norman pentiz, penthouses
Origin: , from Old French apentiz, penthouse
Origin: , from apent
Origin: , past participle of apendre, to belong, depend
Origin: , from Medieval Latin appendere
Origin: , from Latin, to hang, suspend; see append. Word History: The word penthouse goes back to Latin appendere, “to cause to be suspended.” In Medieval Latin appendere developed the sense “to belong, depend,” a sense that passed into apendre, the Old French development of appendere. From apent, the past participle of apendre, came the derivative apentiz, “low building behind or beside a house,” and the Anglo-Norman plural form pentiz. The form without the a- was then borrowed into Middle English, giving us pentis (first recorded about 1300), which was applied to sheds or lean-tos added on to buildings. Because these structures often had sloping roofs, the word was connected with the French word pente, “slope,” and the second part of the word changed by folk-etymology to house, which could mean simply “a building for human use.” The use of the term with reference to fancy apartments developed from its application to a structure built on a roof to cover such things as a stairway or an elevator shaft. Penthouse then came to mean an apartment built on a rooftop and finally the top floor of an apartment building.
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