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Hyphens, En Dashes, Em Dashes
Q. What is correct style: “X and Y axes” or “X- and Y-axes”?
A. In the context of the Cartesian coordinate system, the hyphens are conventional: “X-axis and Y-axis” or “X- and Y-axes.” But unless the axes have been specifically labeled with capital letters, they are usually referred to as the x- and y-axes. In nonmathematical contexts (e.g., to refer to a simple chart or graph), the hyphens are often omitted, as in “x and y axes,” which has the advantage of not requiring a suspended hyphen. Consider your context and be consistent. For suspended hyphens, see CMOS 7.88; for math, see chapter 12.