function keyn. One of a set of keys on a computer keyboard that execute a function within a given application and are usually numbered 1 through 12.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.function key n (Computer Science) computing a key on the keyboard of a microcomputer, etc. that gives special commands to the computer Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014func?tion key` n. a key on a computer keyboard used alone or with other keys for operations. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.