Also found in: Encyclopedia.
Related to semidiurnal: ebbed
1. Of, relating to, occurring, or performed during half a day.
2. Occurring or coming approximately once every 12 hours, as the tides.
3. Of or relating to the arc described by a celestial body between its meridian passage and its points of rising or setting.
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.
1. of or continuing during half a day
2. occurring every 12 hours
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
sem•i•di•ur•nal(ˌsɛm i daɪˈɜr nl, ˌsɛm aɪ-)
1. pertaining to, consisting of, or accomplished in half a day.
2. occurring every 12 hours or twice each day.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.