Bloodhound

n. dog with an acute sense of smell (used for tracking and hunting)

A Bloodhound (also known as the St. Hubert Hound) is a large breed of dog bred for the specific purpose of tracking human beings. Consequently, it is often used by authorities to track escaped prisoners or missing persons. It is a scenthound, famed for its ability to follow a scent hours or even days old, over long distances. Combining a keen sense of smell with a tenaciously strong tracking instinct, bloodhounds have proven their worth as the archetypal trailing dog.
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Noun
1. a breed of large powerful hound of European origin having very acute smell and used in tracking
(synonym) sleuthhound
(hypernym) hound, hound dog

n. sleuth, sleuthhound

(n.)
A breed of large and powerful dogs, with long, smooth, and pendulous ears, and remarkable for acuteness of smell. It is employed to recover game or prey which has escaped wounded from a hunter, and for tracking criminals. Formerly it was used for pursuing runaway slaves. Other varieties of dog are often used for the same purpose and go by the same name. The Cuban bloodhound is said to be a variety of the mastiff.