Y chromosome or Y-chro·mo·some (w??kr??m?-s?m?)n. The sex chromosome associated with male characteristics in mammals, not occurring in females and occurring with one X chromosome in the male sex-chromosome pair.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-chromosome n (Biology) the sex chromosome that occurs as one of a pair with the X-chromosome in the diploid cells of the males of many animals, including humans. Compare X-chromosome Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Y-chro·mo·some (w??kr??m?-s?m?) The sex chromosome that is paired with an X-chromosome in males.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.