Definition of "penthouse"
(now historical) A structure or annexe (especially one with a sloping roof) extending from the side of a building, sometimes as protection from the weather.
Quotations
At length, recommending himself to God, he let go one end of his cord, and suffered himself to fall down upon an old shed or penthouse, which, with the weight of his body, fell in with great noise.
1826, William Eusebius Andrews, Review of Fox's Book of Martyrs, WE Andrews, pages 386–7
verb
third-person singular simple present penthouses, present participle penthousing, simple past and past participle penthoused