Diurnal Di*ur"nal, 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. (Zo["o]l.) 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]

The Collaborative International Dictionary of English. 2000.