Английский Этимологический словарь - period

- early 15c., from M.L. periodus "recurring portion, cycle," from L. periodus "a complete sentence," also "cycle of the Greek games," from Gk. periodos "rounded sentence, cycle, circuit," lit. "going around," from peri- "around" + hodos "a going, way, journey." Meaning "dot marking end of a sentence" first recorded 1609, from similar use in M.L. Sense of "menstruation" dates from 1822. Periodical "magazine that publishes regularly" is from 18c. Sense of "repeated cycle of events" led to that of "interval of time." Periodic table in chemistry is from notion of the arrangement, in which similar properties recur at intervals in elements in the same area as you read down the rows of the table.