E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A blood-hound which follows the sleuth or track of an animal. (Slot, the track of a deer, is the Anglo-Saxon slting, Icelandic, sloth, trail; Dutch, sloot.)
There is a law also among the Borderers in time of peace, that whose denieth entrance or sute of a sleuth-hound in pursuit made after fellons and stolen goods, shall be holden as accessarie unto the theft.Holinshed: Description of Scotland, p. 14.