Formerly used as a treatment to reduce excess blood (one of the four humors of medieval medicine). blood letting

ETYM Latin phlebotomia, Greek; phlebos a vein + temnein to cut: cf. French phlébotomie. Related to Fleam.
The act or practice of opening a vein for letting blood, in the treatment of disease; bloodletting; bleeding.
Blood-letting; venesection.