Definition of diurnal

• a. - Relating to the daytime; belonging to the period of daylight, distinguished from the night; -- opposed to nocturnal; as, diurnal heat; diurnal hours.
• a. - Daily; recurring every day; performed in a day; going through its changes in a day; constituting the measure of a day; as, a diurnal fever; a diurnal task; diurnal aberration, or diurnal parallax; the diurnal revolution of the earth.
• a. - Opening during the day, and closing at night; -- said of flowers or leaves.
• a. - Active by day; -- applied especially to the eagles and hawks among raptorial birds, and to butterflies (Diurna) among insects.
• a. - A daybook; a journal.
• a. - A small volume containing the daily service for the "little hours," viz., prime, tierce, sext, nones, vespers, and compline.
• a. - A diurnal bird or insect.