period (n.)

early 15c., periode, "a course or extent of time; a cycle of recurrence of a disease," from Old French periode (14c.) and directly from Medieval Latin periodus "recurring portion, cycle," from Latin periodus "a complete sentence," also "cycle of the Greek games," from Greek periodos "cycle, circuit, period of time," literally "a going around," from peri "around" (see peri-) + hodos "a going, traveling, journey; a way, path, road," a word of uncertain origin (see Exodus).

Sense of "repeated cycle of events" led to that of "interval of time." From 1712 as "an indefinite part of any continued state or series of events;" by 1727 as "time in which a circuit or revolution (as of a heavenly body) is made." Sense of "episode of menstruation" is by 1829, probably short for period of menstruation (1808), etc..  

The meaning "dot marking end of a sentence" is recorded c. 1600, from the earlier sense of "a complete sentence, from one full stop to another," then "a full pause at the end of a sentence" (1580s). The educational sense of "portion of time set apart for a lesson" is from 1876. The sporting sense "division of a game or contest" is attested by 1898. As an adjective from 1905; period piece is attested from 1911.

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Definitions of period from WordNet

period (n.)
an amount of time;
Picasso's blue period
hastened the period of time of his recovery
a time period of 30 years
Synonyms: time period / period of time
period (n.)
the interval taken to complete one cycle of a regularly repeating phenomenon;
period (n.)
(ice hockey) one of three divisions into which play is divided in hockey games;
period (n.)
a unit of geological time during which a system of rocks formed;
ganoid fishes swarmed during the earlier geological periods
Synonyms: geological period
period (n.)
the end or completion of something;
a change soon put a period to my tranquility
death put a period to his endeavors
period (n.)
the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause; "a woman does not take the gout unless her menses be stopped"--Hippocrates; "the semen begins to appear in males and to be emitted at the same time of life that the catamenia begin to flow in females"--Aristotle;
Synonyms: menstruation / menses / menstruum / catamenia / flow
period (n.)
a punctuation mark (.) placed at the end of a declarative sentence to indicate a full stop or after abbreviations;
in England they call a period a stop
Synonyms: point / full stop / stop / full point