gap junctionn. An intercellular network of protein channels that facilitates the cell-to-cell passage of ions, hormones, and neurotransmitters.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.gap? junc`tion n. Biol. a structure consisting of a series of channels extending across the gap between two cells, allowing the passage of ions, small molecules, etc. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.