ichneumon (n.) Look up ichneumon at Dictionary.com
1570s, "weasel-like animal of Egypt," from Latin ichneumon, from Greek ikhneumon "ichneumon," literally "searcher, tracker," perhaps so called because it hunts crocodile eggs, from ikhneuein "hunt for, track," from ikhnos "a track, footstep, trace, clue," of unknown origin. Used by Aristotle for a species of wasp that hunts spiders (a sense attested in English from 1650s).