\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.
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.
         Ere twice the horses of the sun shall bring Their
         fiery torcher his diurnal ring.       --Shak.
3. (Bot.) Opening during the day, and closing at night; --
   said of flowers or leaves.
4. (Zo["o]l.) Active by day; -- applied especially to the
   eagles and hawks among raptorial birds, and to butterflies
   (Diurna) among insects.
{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}.

\Di*ur"nal\, n. [Cf. F. diurnal a prayerbook. See
{Diurnal}, a.]
1. A daybook; a journal. [Obs.] --Tatler.
2. (R. C. Ch.) A small volume containing the daily service
   for the ``little hours,'' viz., prime, tierce, sext,
   nones, vespers, and compline.
3. (Zo["o]l.) A diurnal bird or insect.