Periodic
mid 17th century: from French périodique, or via Latin from Greek periodikos ‘coming round at intervals’, from periodos (see period).
wiktionary
From French périodique, from Medieval Latin periodicus(“cyclical”), from Latin periodus(“complete sentence, period, circuit”), from Ancient Greek περίοδος(períodos, “cycle, period of time”). Equivalent to period + -ic.
From per- + iodic.
etymonline
periodic (adj.)
"proceeding in a series of successive revolutions; pertaining to or of the nature of a cycle or period" 1640s, from French périodique (14c.), from Late Latin periodicus "that returns at stated intervals of time," from Latin periodus "recurring portion, cycle" (see period). From 1660s as "occurring at regular intervals of time."
The periodic table in chemistry (1889) is so called for the arrangement, in which similar properties recur at intervals in elements in the same area as you read down the rows of the table. This sense of the word is attested from 1872 (periodic law).
