mix-up also mix·up (m?ks??p?)n.1. A state or an instance of confusion; a muddle: a bureaucratic mix-up.2. Informal A fight or melee.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.mix-up n 1. a confused condition or situation 2. informal a fight vb (tr, adverb) 3. to make into a mixture: to mix up ingredients. 4. to confuse or confound: Tom mixes John up with Bill. 5. (often passive) to put (someone) into a state of confusion: I’m all mixed up. 6. (foll by: in or with; usually passive) to involve (in an activity or group, esp one that is illegal): why did you get mixed up in that drugs racket?. 7. mix it up informal US and Canadian to fightCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014mix-up (?m?ks??p) n. 1. a state of confusion. 2. a fight. [1835?45] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.