Q: While friends of ours were telling us about their honeymoon, someone asked where this term comes from. Do you know? – R.P., Cerritos, Calif.

A: It has been theorized that our word “honeymoon” derives from the Scandinavian custom of drinking honeyed wine during the first month (or “moon”) of connubial existence. But while ancient northern Europeans did enjoy such a drink, there is no evidence to suggest that they observed the custom of the honeymoon as we know it.

As far back as 1546, when the term first appeared in print, people recognized the inconstant nature of married life. The “moon” in “honeymoon” is believed to represent a comparison between the fleeting joy experienced by newly married couples and the changing moon, which begins to wane soon after it enters its full phase. The “honey” in “honeymoon,” then, would carry the meaning of “sweet” or “dear.” Thus, a honeymoon would be a period of sweetness that lasted about as long as a full moon.

It wasn’t until the early 1800s that the term came to refer to the vacation taken by married couples after their wedding. Today, the term “honeymoon” is associated both with the trip and the period of joy. The latter sense even appears outside of the context of marriage, as in this example from our files: “MPs fear that the honeymoon between the troops and the civilians might be over.”

Q: Where did the expression “rule of thumb” come from? – J.C., Holly Ridge, N.C.

A: For all its frequent use today, “rule of thumb” is a very old expression. Its first recorded use in print was in 1692, in a volume titled “The Compleat Fencing-Master,” by Sir William Hope, who wrote, “What he doth, he doth by Rule of Thumb, and not by Art.” So even the first recorded use is a general one; it does not refer to any specific rule or any literal use of the thumb.

There are several stories sometimes mentioned to account for the origin of “rule of thumb,” and though they are interesting, we don’t really have sound backing for any of them. One very dubious story tells of a supposed old law, the Rule of Thumb, which allowed the switch a man used to beat his wife to be no larger than the width of his thumb. Another attributes the phrase to the practice of brewers, who would test the temperature of their vats by dunking a thumb. A third story connects the phrase with use of thumb as a ruler. A man’s thumb, at the first knuckle, is typically about an inch across.

This column was prepared by the editors of Merriam-Webster’s Collegiate Dictionary, Tenth Edition. Readers may send questions to Merriam-Webster’s Wordwatch, P.O. Box 281, 47 Federal St., Springfield, MA 01102.