Is drinking-jack another word for mug?

In "Tower of the Elephant", Robert E. Howard uses the word "drinking-jack" three times apparently meaning mug or something like that, judging by the context:

Torchlight licked luridly from broken windows and wide-thrown doors, and out of those doors, stale smells of wine and rank sweaty bodies, clamor of drinking-jacks and fists hammered on rough tables, snatches of obscene songs, rushed like a blow in the face.

'Then give ear and learn wisdom, fellow,' said he, pointing his drinking-jack at the discomfited youth.

Ale splashed over the jack's lip, and the Kothian roared in fury, dragging at his sword.

However I can find no meaning which fits in any dictionary or anywhere else. I know that he was from Texas and lived from 1906 to 1936, so is this a Texan colloquial term or something? Does it even mean mug or am I misunderstanding it?

Solution 1:

Although no longer in common use, the OED defines a sense for "jack" meaning a drinking vessel that dates back to the 1500s. It is described as English regional, but being an older word, it's not too surprising that it would pop up in Texas.

22. A vessel for holding liquid, esp. alcohol. Also: a drinking vessel, typically of waxed leather coated outside with tar or pitch; a tankard. Now historical and English regional (northern).

Though it is described as "historical," citations are provided as recently as 2003.

2003 P. Finney Gloriana's Torch 69 Becket..went in search of booze, which he found in the jack of spiced ale.

It is cross-referenced with "black jack," which is also listed as historical. Public dictionaries like Merriam-Webster have definitions for "black jack" as a drinking vessel (see definition 3 in M-W).

Neither the OED nor other sources I checked provide an etymology for the word "jack" in this sense, though it seems notable that "jack" has been used to refer to numerous implements and devices, frequently in compounded form, like boot-jack, winding-jack, carriage-jack, etc.