- Happening during the day - Of or during the daytime - Relating to the daytime; belonging to the period of
daylight, distinguished from the night; -- opposed to nocturnal; as,
diurnal heat; diurnal hours. - 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. - Opening during the day, and closing at night; -- said of
flowers or leaves. - Active by day; -- applied especially to the eagles and
hawks among raptorial birds, and to butterflies (Diurna) among insects. - A daybook; a journal.