cloud

From Middle English cloud, from Old English clūd, meaning a mass of stone, a rock, or a boulder. This traces back through Proto-West Germanic *klūt and Proto-Germanic *klūtaz/*klutaz ("lump, mass, conglomeration") to the Proto-Indo-European root *gel-, "to ball up, clench."

The Old English word meant a solid lump of rock or a hill, not a wisp of vapor in the sky. Over time it came to describe the puffy, mass-like shapes overhead, eventually pushing out the older Old English word for cloud, wolcn (which survives today as "welkin").

It's related to English clod, clot, clump, and club — all words that carry that same old sense of a rounded lump or mass.