- The horizontal axis of a two-dimensional Cartesian coordinate system. (noun)
- One of three axes in a three-dimensional Cartesian coordinate system. (noun)
- A reference axis, usually horizontal, of a graph or two- or three-dimensional Cartesian coordinate system along which the x-coordinate is measured (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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