Pavilion ("a building with open sides") comes from Anglo-Norman pavilloun, from Old French paveillon, which in more recent times had the same meaning but once meant "butterfly". Yes, you read that right; this curious change in definition arose because the original pavilions, which were tents, bore some kind of a resemblance to butterfly wings, enough to merit such a name. It was too early at this point for the "butterfly" translation to enter English, but it did survive as the modern French word papillon (itself the precursor of the dog breed papillon, literally "butterfly"). Anyway, All this goes back to the Latin word papillionem, which doubled in meaning as "butterfly" and "moth", which comes from Proto-Indo-European pal, "to touch". Usage of both papillon and pavilion have plateaued over time. Next time you're at a company picnic or something, make sure your covered area doesn't fly away.
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.