Per`i*od"ic (?), a. [Pref. per- + iodic.] Chem. Pertaining to,
derived from, or designating, the highest oxygen acid (HIO) of
iodine. © Webster 1913. Pe`ri*od"ic (?), Pe`ri*od"ic*al (?), a.
[L. periodicus, Gr. : cf. F. p'eriodique.] Of or pertaining to a
period or periods, or to division by periods. The
periodicaltimes of all the satellites. Sir J. Herschel.
Performed in a period, or regular revolution; proceeding in a
series of successive circuits; as, the periodical motion of the
planets round the sun. Happening, by revolution, at a stated
time; returning regularly, after a certain period of time;
acting, happening, or appearing, at fixed intervals; recurring;
as, periodical epidemics. The periodic return of a plant's
flowering. To influence opinion through the periodical press. Of
or pertaining to a period; constituting a complete sentence.
Periodic comet Astron., a comet that moves about the sun in an
elliptic orbit; a comet that has been seen at two of its
approaches to the sun. -- Periodic function Math