And thanks for all the toast.

Dear Word Detective:  Where did the term “bread and butter letter” originate?  I do know that it is a “thank you” letter for staying in someone’s house. — Leslie Player.

Well, you’re one step ahead of me.  I thought I had never heard the term “bread and butter” used in that sense before, but then I vaguely remembered, in my childhood, hearing an older person using it.  I suppose I should have asked what it meant, but at that age I regarded it as just one more grownup mystery, like property taxes and why in the world any sane person would eat eggplant.  I still haven’t figured out the second one.

“Bread,” being the staff of life and all, is, of course, a very old word, though it’s interesting to note that in Old English the word simply meant “piece of food, morsel,” not necessarily the stuff cranked out by Pepperidge Farm.  “Butter” is even older, and comes from the Greek “boutyron,” meaning literally “cow cheese.”  By the way, that “staff of life” business comes from the Bible, where “to break the staff of bread” means to cut off the food supply that supports a people (as a walking staff supports an individual).

“Bread and butter” has been used, since at least the early 18th century, to mean  “everyday kinds of food” (”It was strictly a bread and butter dinner, not a snail in sight”), but more often in a figurative sense to mean “means of living, basic financial support,” often of a distinctly unglamorous sort (”Sure, I dabble in tech stocks, but repossessing cars is my bread and butter”).

The logic of “bread and butter letter,” a term first appearing in print in the US in the early 20th century, seems to fall somewhere between those two uses.  The writer is thanking his or her hosts for their hospitality (and food), but the letter is also a basic social formality, not likely to contain any exciting content.  A “bread and butter” note may not be eagerly awaited, but it’s the sort of thing expected and probably noticed most in its absence.

Speaking of bread and butter, I noted a few years back that my wife Kathy had grown up in Ohio with the tradition of saying “bread and butter” whenever an object (parking meter, UFO, whatever) or another person comes between you and your walking companion.  At first I was mystified, but it turns out to be a common childhood ritualistic incantation in the American Midwest, invoking the togetherness of bread and butter to insure that the two companions are not separated for longer than a moment.