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.-a small volume containing the daily service for the "little hours," viz., prime, tierce, sext, nones, vespers, and compline.-a diurnal bird or insect.