Now, here’s a look at six books that cut the mustard.

Uh — they cut the mustard? How many times have you said that? Maybe, oh, countless? Me too. Even so, while I regularly spread the mustard, I don’t actually cut the mustard, or the mustard seed.

I could cut mustard greens, but then I’d have to call this a piece about six books that cut the mustard greens. Nah.

Such are the vagaries of our language. Not only do we regularly use it and abuse it — and from those abuses, a living language continues to breathe and evolve — but we constantly say stuff we are unable to explain.

Often, there is an explanation. English, that greatest and most flamboyant of thieves, often leaves clear tracks in its pilferage, and they swirl in mazes of strange idea associations and pronunciation shifts back through the centuries and directly to the tongues of the original owners. (Tongue is an example: from the French langue. Before that, the Latin lingua. Before that from dinghu of Indo-European languages. Dinghu? Don’t ask. We’ll never get to the books.)

For other words and phrases, the origins are lost. Maybe the reason we still cut the mustard when we’re successful at something is because the sound of it tracks nicely.

“In America, to say something was ‘the proper mustard’ in the early 20th century meant it was the genuine article, and ‘cutting the mustard’ became a popular idiom to describe something that was up to scratch and more,” writes Susie Dent in “What Made the Crocodile Cry? 101 Questions About the English Language” (Oxford University Press, $18.95). Her fun book comes from the folks who continue to print the remarkable Oxford English Dictionary — about English eccentricities that we’ve turned into everyday language. She also writes that, alas, the precise origin of any form of the phrase is lost. Which doesn’t mean that cut the mustard doesn’t make sense figuratively just because its essence is lost literally.

But what about that up to scratch that Dent used to define the phrase in question? For the answer, I turned to John Ayto’s “From the Horse’s Mouth: Oxford Dictionary of English Idioms” (Oxford University Press, $21.95), the third edition of a dictionary of idioms. Turns out that we do know the origin of up to scratch, which Ayto, who edited the dictionary, attributes to the sports world.

The scratch, he tells us, was the mark from which competitors began a race unless they’d been given an advantage, and could start ahead of the mark. So a competitor starting from scratch (there’s another one!) began the competition without any advantage. And up to scratch? “A competitor who was up to scratch was of a good enough standard to start a race,” Ayto writes.

His idiom book is essentially a typical dictionary — an index long on definitions and with a nod to etymologies — but the phrase origins he cites are often surprising or just plain interesting, the sorts of things you store in some mental file folder, and who knows when you’ll use them.

For example, I looked up one of my favorite words, fly, the muscular workhorse of only three letters that has so many meanings, without being used in idioms, that it’s a clear example of both the versatility and difficulty of English. Fly and its variants take up all of page 134, and I was particularly struck by fly in the ointment, a phrase that conjures a perfect image.

I learned this, which fascinated me: “This expression alludes to Ecclesiastes 10:1: ‘Dead flies cause the ointment of the apothecary to send forth a stinking savour.'”

A third new Oxford release — they get lots of mileage out of their words over there — is called “The Insect That Stole Butter? Oxford Dictionary of Word Origins” (Oxford University Press, $21.95), which I spent many hours with because I became glued. It’s a dictionary of word origins, and, abracadabra (first recorded in an A.D. 2 Latin poem), it cast a spell on me. Something as simple as learning that a cupboard was originally a single table for the display of cups, what we now call a sideboard, sent me scrambling for other words that once had literal meanings.

And then I got to words with odd origins: pedigree, for example, from the French spoken by Norman settlers in England: pe de grue, a crane’s foot. “In medieval manuscripts,” explains the book’s editor, Julia Cresswell, “a mark consisting of three curved lines was used to indicate a person’s family descent or succession. People saw a resemblance between this mark and the claw of a crane.” Who knew?

It’s easy to see, after a few examples, the market for these books. Every language both shapes, and is shaped by, the way its speakers think. Every time we speak or write in English, we think within its pushable boundaries. These books are a glimpse into the way we shape ideas and make connections — and they make it easy to become gung-ho on words.

As for gung-ho, Ralph Keyes points out in his new “I Love It When You Talk Retro: Hoochie Coochie, Double Whammy, Drop a Dime, and the Forgotten Origins of American Speech” (St. Martin’s Press, $25.95) that it was the motto of a New Zealand group, taken from the Chinese words kung and ho — work and together. A colonel in the South Pacific adopted it for his Marine battalion, and a 1943 movie made that battalion’s story popular — and also the phrase. “Over the years,” Keyes writes, “gung-ho took on an odor of overzealousness. Nowadays, calling someone ‘real gung-ho’ isn’t necessarily a compliment.”

Times change, meanings too. Keyes’ book is full of phrases, most still in use, whose origins are not what we might think, and some really take the cake — a phrase originally used after the Civil War by freed slaves to refer to the cake they’d give the winner of a dance competition that mocked the marches in plantation balls.

Write about words, and people think you’re a walking encyclopedia of cool stories. Write about grammar and no matter what you say, someone will hate you. (English class students, always, to name many someones.) We’re not as protective of our tongue as the French, but we’ll still fight not to split an infinitive ever. Or if we like, to always split one.

For guidance that explains grammar in a precise understandable fashion, Janis Bell’s “Clean, Well-Lighted Sentences: A Guide to Avoiding the Most Common Errors in Grammar and Punctuation” (Norton, $13.95) works just fine. It’s a no-nonsense grammar, with quizzes after each chapter and solid examples, and while it doesn’t address splitting infinitives, you’ll come out of it knowing all the basics of tense and case and even punctuation use.

If you already know all that and like to write (or speak), pick up the extraordinary “Woe Is I: The Grammarphobe’s Guide to Better English in Plain English” (Riverhead, $22.95) by Patricia T. O’Conner, in its new third edition. O’Conner, a former editor at The New York Times Book Review, is among American English’s smartest grammarians — and she writes about grammar as if she’s wrangled you into a conspiracy to put common sense above anyone’s rules.

This seems a bold idea, because logic has little to do with the way language works, but the more I read O’Conner — and believe me, “Woe Is I” is a grammar that reads like a conversation — I realized that common sense has everything to do with the way we use English, no matter how the language is supposed to work.

And she makes it so easy to be sensible. One chapter of “tombstones” is about all the dead rules we’ve long broken but many people still insist on. (There, I just broke one.) O’Conner speaks not for an anarchy, with a language so imprecise it’s meaningless, but for one that lives overtime because people in general, and not just grammarians, make it work.