a. [ L. diurnalis, fr. dies day. See Deity, and cf. Journal. ] 1. Relating to the daytime; belonging to the period of daylight, distinguished from the night; -- opposed to nocturnal; as, diurnal heat; diurnal hours. [ 1913 Webster ]

2. 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. [ 1913 Webster ]

Ere twice the horses of the sun shall bring
Their fiery torcher his diurnal ring. Shak. [ 1913 Webster ]

3. (Bot.) Opening during the day, and closing at night; -- said of flowers or leaves. [ 1913 Webster ]

4. (Zool.) Active by day; -- applied especially to the eagles and hawks among raptorial birds, and to butterflies (Diurna) among insects. [ 1913 Webster ]

Diurnal aberration (Anat.), the aberration of light arising from the effect of the earth's rotation upon the apparent direction of motion of light. --
Diurnal arc, the arc described by the sun during the daytime or while above the horizon; hence, the arc described by the moon or a star from rising to setting. --
Diurnal circle, the apparent circle described by a celestial body in consequence of the earth's rotation. --
Diurnal motion of the earth, the motion of the earth upon its axis which is described in twenty-four hours. --
Diurnal motion of a heavenly body, that apparent motion of the heavenly body which is due to the earth's diurnal motion. --
Diurnal parallax. See under Parallax. --
Diurnal revolution of a planet, the motion of the planet upon its own axis which constitutes one complete revolution.

Syn. -- See Daily. [ 1913 Webster ]

n. [ Cf. F. diurnal a prayerbook. See Diurnal, a. ] 1. A daybook; a journal. [ Obs. ] Tatler. [ 1913 Webster ]

2. (R. C. Ch.) A small volume containing the daily service for the “little hours, ” viz., prime, tierce, sext, nones, vespers, and compline. [ 1913 Webster ]

3. (Zool.) A diurnal bird or insect. [ 1913 Webster ]

n. A journalist. [ Obs. ] Bp. Hall. [ 1913 Webster ]

adv. Daily; every day. [ 1913 Webster ]

n. The quality of being diurnal. [ 1913 Webster ]