Old English læce, physician, appears some 225 times in the surviving corpus, Gothic lekeis, Old High German lahhi alongside; the worm word appears only a handful of times, glossing Latin sanguisuga and hirudo. The dictionaries split the file: the OED suspects a separate etymon for the worm, folk-etymologized into the doctor word because doctors applied leeches; the alternative derives both from Proto-Germanic roots, the physician from a Celtic liaison, Old Irish liaig. By the ninth century a gloss already uses læce for the healer beside hirudo, so the pun predates the confusion. Physician-leech was archaic by 1700, but the worm kept the title, Hirudo medicinalis, the medical one.
The bloodletting centuries made the merger literal: the leech was the instrument, applied by the læce, and the profession's reputation rode on how much blood the tool removed, the barber-surgeons' basin and the worm doing the same prescription. The folk verdict embedded itself in the language permanently: a leech is a person who drains you, attached and silent, and the therapy was judged by the same metaphor, medicine as sanctioned parasitism. Modern microsurgery quietly re-hired the worm, leech therapy for reattached fingers, the parasite back on staff with an FDA clearance, no longer a metaphor.
The claim: the læce-leech merger is the archive's favorite case of the vocabulary keeping the receipt, the patient's-eye view fossilized in the word itself, the healer and the drainer as one noun, because the fee and the blood left the body by the same route, and every subsequent name for the profession, doctor, teacher, physician, nature-knower, is the worm-word cleaned up for the waiting room. Verdict: the corpus supports the overlap, not the motive, and the archive files the motive under stories with the note that the metaphor has outlived every professional rebrand. The worm got honest work in the end. The name never got an honest answer. Six hundred years of dictionaries cannot say which sense drained the other, which is, the archive submits, the correct diagnosis.
If the healer and the parasite shared a name for six centuries, what did the language know that the patients suspected?