from The Century Dictionary and Cyclopedia
- n. A jug made of leather; a black-jack.
- n. Any species of the genus Oligoplites, fishes of the family Carangidæ.
Sorry, no etymologies found.
Like many of the patrons here, he had his own mug, a leather-jack, tarred on the inside to make it waterproof and kept tied to his waist when not in use.