Math is hard for many people, though it’s often not the numbers that cause so many problems, but the words accompanying them or standing in for them.

Many words have numbers embedded in them, which can give you a clue as to what they mean. A “pentagram,” for example, is a five-sided star; “penta” means “five.” Similarly, a “bi” prefix usually means “two” (biennial), though watch out for the “biweekly” confusion. “Quad” means “four” (quadruplets); (“octo” means “eight” (octopus). When you get to “ten,” some confusion can set in. The prefix “dec” swings both ways around the number 10. Add an “a,” and you have “decade,” 10 years. Add an “i,” though, and you have words like “decimal.” The number it represents is indeed based on 10, but as a fraction of 10, not a multiplier, as in “octo” and the others.

Sometimes that number is ignored. “Decimate” used to mean the same as “tithe,” or give one-tenth of your income to the church. It also used to mean “to select by lot and kill every tenth one,” a punishment used by Rome against rogue legionnaires. For many years, as we’ve written before, careful usage limited its use to mean the destruction of one-tenth of something, but eventually it came to mean “destroy a large portion of.” That’s fully acceptable English now, but you can’t use it when there’s only a few things available to be destroyed, or when another proportion is given. Garner’s Modern American Usage suggests avoiding it completely because “the word is infected with ambiguity.”

Ambiguous, too, is the phrase “order of magnitude.” As The New York Times Manual of Style and Usage says: “In mathematics, an order of magnitude means multiplication by 10; several orders of magnitude means a quantity multiplied by hundreds or thousands. As a way of saying something has increased a great deal, it has become a cliché.” It’s frequently used, correctly, when dealing with computer processing power, which has increased by “orders of magnitude.” But can a scandal involving an elected official increase “the political heat by an order of magnitude,” as one news report said? Instead of using a phrase that has such precise scientific and mathematical meaning to discuss something not really measurable, substitute something more mundane, like “a lot.”

We’ve also already dealt with the “times greater” (or less) and “-fold” issue. Suffice it to say that it’s complicated, and you’re better off sticking with “double” or “triple,” or just giving the numbers themselves, to be sure everyone understands what you’re saying.

Next week, we’ll talk about some simple ways to make large numbers easier for you—and your readers.

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Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years.