Definition of "diurnal" [di•ur•nal]

• Relating to or occurring in a 24-hour period; daily. (adjective)
• Occurring or active during the daytime rather than at night: diurnal animals. (adjective)
• Botany Opening during daylight hours and closing at night. (adjective)
• A book containing all the offices for the daily canonical hours of prayer except matins. (noun)
• Archaic A diary or journal. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Apparently, McLeanian logic tells us that the rotation of the earth also explains the seasons, considering how well it correlates with the short-term diurnal variation..."
• "There is also a great difference between day and night high water; the difference between them is called the diurnal tide."
• "God then willed the revolution of the outermost sphere, known as the diurnal sphere, which caused all the other spheres to revolve with it, thereby producing changes in the hyle in accordance with the motions of the sphere."