Where does the word “leech” come from and What does leech mean?

From early English antiquity a physician has been called a leech, and from equally early times physicians have used the aquatic bloodsucking worm, known as leech, for bloodletting under certain conditions.

It is impossible to tell which was first to receive the name.

Etymologists believe, however, that present identity of spelling is accidental and that, originally, the words were different, although of similar form.

They think also that through the use by the early physician of the worm for bloodletting, the name of the latter became altered to that of the physician through association.