Unix or UNIX (yo?o?n?ks) A trademark for a computer operating system that allows multiple simultaneous users.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.UNIX (?ju?n?ks) n (Computer Science) a multi-user multitasking operating system found on many types of computerCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014UNIX (?yu n?ks) Trademark. a multiuser, multitasking computer operating system. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.