The term leech when referring to parasites has its origins in the year 900 CE, spelled as lyce (later variations included laece, liche, leche, leach, and more). It is commonly believed to have stemmed from another Old English word spelled as leech around the same time period, meaning “doctor”. However, according to the Oxford English Dictionary, the latter word merely influenced the spelling of the former through folk etymology, and the term for the worm actually originated from the Middle Dutch lake, also signifying “leech”. This is likely a cognate of the English word lake, as both have roots in the Proto-Germanic term lako, which described bodies of water. If this is accurate, it can be traced back to the Proto-Indo-European reconstruction leg, which denoted “leak” or “drain”.
