clog

The origin of "clog" is unknown, but it may come from Middle English "clog," a weight fastened to an animal's leg to slow it down. That word may in turn trace back to a North Germanic root, Proto-Germanic *klumpô, meaning "lump" or "mass."

The facts don't describe a documented shift in meaning, only a possible origin as a leg-weight used to hinder movement — a sense that fits naturally with today's use for anything that blocks or slows something down.

It may be related to Old Norse "klugu" or "klogo," meaning a knotty tree log, and to Dutch "klomp," both pointing back to the same idea of a heavy lump.