bloodhound

Etymology

From Middle English blodhound, blodhond; equivalent to blood + hound. Cognate with Dutch bloedhond (“bloodhound”), Middle Low German blōthunt (“bloodhound”), German Bluthund (“bloodhound”), Danish blodhund (“bloodhound”), Swedish blodhund (“bloodhound”). The detective sense follows from the dog's ability to follow a trail.

noun

1. A large scenthound famed for its ability to follow a scent many days old, over vast distances. This dog is often used as a police dog to track missing people, fleeing suspects, or escaped prisoners.
2. (figurative) A detective or other person skilled at finding people or clues.
3. (archaic) A bloodthirsty person.