Learn English – What did the master mean by: “Then thou shalt drink!”

As suggested by the following extract, the original usage of Master dates back to Old English:

The original sense in English is that of a man with authority or control over others. It appears as early as c.897 in Alfred’s translation of Gregory’s Pastoral Care:

• "Thonne he gemette tha scylde the he stieran scolde, hrædlice he gecythde thæt he wæs magister & ealdormonn."

It later developed also into a title of respect, which was later replaced by Mister:

• Master was used in England for men of some rank, especially "free masters" of a trade guild and by any manual worker or servant employee addressing his employer (his master), but also generally by those lower in status to gentlemen, priests, or scholars. In the Elizabethan period, it was used between equals, especially to a group ("My masters"), mainly by urban artisans and tradespeople. It was later extended to all respectable men and was the forerunner of Mister.

The earliest usages as a title to refer to a boy dates back to the early 16th century:

• The use of master as a title goes back to Old English. But the use of master as a title for a boy or a young man is also from the early 16th century. From c.1533-34 in letter by an H. Dowes:

• It pleased your Maistershipp to give me in charge not onlie to give diligent attendaunce uppon Maister Gregory.

This usage as a title for boys survived though centuries also after Mister was introduced, even though it is now considered archaic:

• After its replacement in common speech by Mister, Master was retained as a form of address only for boys who have not yet entered society.

• By the late 19th century, etiquette dictated that men be addressed as Mister, and boys as Master.

Current usages:

In the United Kingdom:

• The use of Master as a prefixed title was, according to Leslie Dunkling, "until recently ... a way of addressing politely a boy who was too young to be called 'Mister'." It was used as a title for the eldest son only; younger sons had no form of address.

In the United States:

• Nancy Tuckerman of the Amy Vanderbilt Complete Book of Etiquette writes that in the USA, unlike the UK, a boy can be addressed as master only until age 12, then is addressed only by his name with no title until he turns 18, when he takes the title of Mr., although it is not improper to use Mr. if he is slightly younger.

(Wordorigins.com/Wikipedia)

It is the second definition listed, therefore less used. I don't believe it is ambiguous in common usage. But as @JanusBahsJacquet says, context is king.

To be absolutely unambiguous, you can use "liege lord" and "liegeman" to refer up and down the allegiance train respectively.