You're under one most of the time, but you never stop to think of the many layers of etymology are contained in the word ceiling. First off, it comes from the Middle English verb ceiling, which was a verb meaning "to panel" (note the -ing at the end). This is from the root ceil, or "to cover", which makes perfect sense considering that that's what a ceiling does. As the soft c and hidden vowel imply, ceil is from Old French, in this case the verb celer, "to conceal", in turn from Latin celare, "to hide", which was sort of modified in meaning because of a little cross-confusion with caelum, "heaven". Anyway, celare comes from Proto-Italic kel, which derives from a reconstructed Proto-Indo-European root which also sounded like kel, and also meant something along the lines of "cover", though it may have varied a bit.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.