y-ax·is (w???k?s?s)n. pl. y-ax·es (w???k?s?z) 1. The vertical axis of a two-dimensional Cartesian coordinate system.2. One of three axes in a three-dimensional Cartesian coordinate system.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved. y-axis n (Mathematics) a reference axis, usually vertical, of a graph or two- or three-dimensional Cartesian coordinate system along which the y-coordinate is measured Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014y-ax?is (?wa??æk s?s) n., pl. y-ax?es (?wa??æk siz) 1. (in a plane Cartesian coordinate system) the axis, usu. vertical, along which the ordinate is measured and from which the abscissa is measured. 2. (in a three-dimensional Cartesian coordinate system) the axis along which values of y are measured and at which both x and z equal zero. [1925?30] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.y-ax·is (w???k?s?s)1. The vertical axis of a two-dimensional Cartesian coordinate system.2. One of the three axes of a three-dimensional Cartesian coordinate system.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.