Description and usage
The ceiling was the upper surface of a room on the inside, separating the room from a room above or from the outside, in which case the ceiling is the inner surface of the roof. See the illustration at Crossbeam, rafter.
Translation
In 2MA 1:16 some translators may find it strange to speak of a hidden door in a ceiling, so it may be necessary to expand the translation or even add a footnote explaining that the priests were, in fact, in a space above the ceiling. They gained access to it through the hidden door.