a bloodsucking leech, Hirudo medicinalis, of Europe, introduced into the northeastern U.S., usually green with brown stripes, up to 4 in. (10 cm) long: once used by physicians to bleed patients.
Main Entry: medicinal leech Function: noun : a large European freshwater leech of the genus Hirudo (H. medicinalis) that is a source of hirudin, is nowsometimes used to drain blood (as from a hematoma), and was formerly used to bleed patients thought to have excess blood
