lǣce

Old English lǣce meant physician, healer, or one who practices medicine. The word predates any association with the worm. Proto-Germanic *lēkijaz meant healer, and it survives in Swedish läkare and Danish læge, both still meaning doctor. In Anglo-Saxon England, the lǣce was the person you called when sickness came.

Because bloodletting was a standard medical treatment — Galen had prescribed it in the second century, and medieval medicine followed Galen religiously — physicians used leeches constantly. The worms were tools of the trade. Over time, the tool acquired the name of the practitioner. By the 1200s, the word leech could mean both the healer and the worm, and context had to sort them out.

The healer meaning faded. By 1600, leech-as-doctor sounded archaic, surviving mainly in compounds like leechcraft (the art of healing). The worm meaning took over completely. One of the oldest English words for a physician was swallowed by the animal it used as an instrument.

Medical leeches made a comeback in the late twentieth century. Surgeons discovered that Hirudo medicinalis could prevent blood clots after microsurgery — the same creature that Galen recommended, useful for different reasons. The FDA approved medicinal leeches in 2004. The Anglo-Saxon lǣce would recognize the practice, if not the paperwork.