thrush

The bird's name comes from Middle English thrusche, blending two Old English words, þrysċe and þræsċe, both tracing back to a Proto-Indo-European root for 'thrush,' *trosdos. The unrelated sense — a mouth or throat infection — has a murky, separate origin, possibly connected to Icelandic þröstur, Danish torsk, or Norwegian trøske.

The bird sense stayed remarkably stable across centuries, always naming the same family of songbirds. The illness sense simply developed alongside it, unconnected in meaning, and its trail goes cold rather than tracing a clear shift.

The bird's ancient root also gave German Drossel, Latin turdus, Russian дрозд, and even Welsh drudwy, meaning starling — a whole flock of cognates across Europe. The illness sense has no confirmed relatives among these; the facts simply don't connect it.