What does the phrase “half seas over” mean and Where does it come from?

The phrase “half seas over” is what we say of a man when we wish to imply that he is pretty thoroughly drunk, not yet under the table and still able to get along, after a fashion, on his own two legs; not quite “three sheets in the wind.”

The English allusion is probably a reference to the likeness between the half canted gait of a man when intoxicated and that of a ship heeled over in the wind, with decks half awash.

But there is also a theory that “half seas over” is an Englishman’s interpretation of the Dutch expression, “op ze zober”, which literally is “oversea beer,” a beer from Holland that was particularly heady and strong.