Leech

A leech, besides a worm, can also sometimes refer to a doctor. The term leech comes from the time when doctors believed leeches could be used to cure a considerable number of diseases. They would apply the leeches to the patient's skin and the blood that the vermin would suck out was regarded as bad, meaning that the person's ailment had gone away. What has always intrigued me is that the word leech bears a striking resemblance to Czech lék and Polish lek "medicine (the one the doctor prescribes)". They ought to be related!