I had a call from my friend Annie, a Belgian linguist who spends a lot of time thinking about idioms. She asked me what I thought "on the up and up" meant. I told her it meant "above board" or "on the level," as in, "Are you sure these intelligence reports are on the up and up?" "Does it mean anything else?," she asked. "Not as far as I know," I told her. "Not so fast," she said -- "go look it up on the Web."

So I googled the phrase, and damned if more half of the first hundred hits for "on the up and up" didn't have it meaning "on the increase," or "improving," as in "Hong Kong's trade is on the up and up." True, a number of these came from sites in the UK and other foreign countries -- it turns out the Brits have been using "on the up and up" like this for more than 70 years. (The OED lists the sense "steadily rising, improving," but no American dictionary has cottoned to it.)

But I was surprised to see how many Americans use the expression that way, too. I found newspaper stories announcing that school activities fees were on the up and up in Minnesota, and that tourism was on the up and up on the Delmarva Penninsula. A defensive end for the Tampa Bay Bucs says that his career is "still on the up and up. . . still on the rise."

Out of curiosity, I sent a question about the item to a discussion group that's peopled by dialectologists and other devotees of word-lore. I had a note back from someone in Berkeley who told me that he was surprised to hear that "on the up and up" could be used to mean "on the increase." But when he asked his wife about it, she said that for her that was the only thing it could mean -- she never knew it could mean "on the level." And what made it odder still was that they've been married for more than twenty years and both grew up in Southern California.

I had this image of the two of them sitting at the breakfast table. He asks "Is your brother's new business on the up-and-up?" and she says, "No, but he's making do." And they go on like that with neither of them ever realizing that they're talking at cross-purposes. Deborah Tannen, call your office.

Of course expressions are always changing their meaning, and every once and a while one of these shifts trips the alarm of the usage buffs, who make a fuss about it. But it's striking how often these disparate meanings can live side-by-side without anybody seeming to notice. What does it mean to say "That gives me heartburn"? I always figured it meant that something made you anxious or worried, but it turns out that a lot of people use it to mean "That makes me furious." I don't know whether that corresponds to a difference in dialect or in diet.

In fact sometimes a word can have contradictory meanings with no one being the wiser. I once got into an argument with a linguist friend over the meaning of the sentence "The pool was deceptively shallow." I maintained that it meant that the pool was shallower than it looked and he said it meant that the pool was deeper than it looked. To settle the argument I took advantage of my role as chair of the usage panel of the American Heritage Dictionary, a group of 175 noted writers that we poll every so often on usage questions. But when we asked the panelists what "The pool is deceptively shallow" means, the results were curiously inconclusive. Half of them said that it means "The pool is shallower than it appears," a third said that it means "The pool is deeper than it appears," and the rest said it could go either way. In other words, if you put that sentence on a warning sign you can be dead certain that anywhere from a third to a half of the people who see it will get the wrong message.

Or take mininal. "She ran best when she had a minimal amount of food in her stomach" -- does that mean she ran best when she'd eaten nothing or when she'd eaten a bit? The usage panel was split on that one, too -- a third said A, a third said B, and another third said it could mean either one.

If you're of a pessimistic turn of mind, you could take all this as a reminder of how elusive understanding can be -- it puts us on guard against what Adrienne Rich called the dream of a common language. But maybe the wonder of it all is that we manage to muddle through, breakfast after breakfast, trusting to good faith to bridge over all the gaps in comprehension. To paraphrase another poet, Randall Jarrell: we understand each other worse, and it matters less, than any of us suppose.