Periods

n. punctuation mark resembling a small dot (the mark . ) placed at the end of a sentence; end; pause at end of a phrase; full sentence

n. menstrual period, menstrual cycle

n. age, era; season; lesson; length of time; (Sports) one of the segments of the playing time of a game (such as quarter, half or overtime)

Period and periodic may refer to:An interval of time that an event, chain of events, instance or happening, takes place within. It is measured between a start point and an end point and generally repeats (which is where the term period came to describe a female's menstrual cycle) or progresses, in a with the end point of one period being the start point of the next.A periodic sentence.A full stop, a punctuation mark which indicates the end of a sentence (.).
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Periods, n.pl horizontal rows of elements within a periodic table. Elements within a period share similar physical and chemical properties. [more]Periods - Community and Resources

Noun
1. an amount of time; "a time period of 30 years"; "hastened the period of time of his recovery"; "Picasso's blue period"
(synonym) time period, period of time
(hypernym) fundamental quantity, fundamental measure
(hyponym) trial period, test period
2. one of three periods of play in hockey games
(hypernym) playing period, period of play, play
3. a stage in the history of a culture having a definable place in space and time; "a novel from the Victorian period"
(synonym) historic period, historical period
(hypernym) time period, period of time
4. the interval taken to complete one cycle of a regularly repeating phenomenon
(hypernym) time interval, interval
(hyponym) orbit period
5. the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause; "the women were sickly and subject to excessive menstruation"; "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
(synonym) menstruation, menses, menstruum, catamenia, flow
(hypernym) discharge, emission, expelling
(hyponym) menorrhagia, hypermenorrhea
6. 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"
(synonym) point, full stop, stop, full point
(hypernym) punctuation, punctuation mark
(hyponym) suspension point
7. a unit of geological time during which a system of rocks formed; "ganoid fishes swarmed during the earlier geological periods"
(synonym) geological period
(hypernym) geological time, geologic time
(hyponym) Quaternary, Quaternary period, Age of Man
(part-holonym) era, geological era
(part-meronym) epoch
8. the end or completion of something; "death put a period to his endeavors"; "a change soon put a period to my tranquility"
(hypernym) end, ending

Precambrian 
Cambrian 
Ordovician 
Silurian 
Devonian 
Carboniferous 
Permian 
Triassic 
Jurassic 
Cretaceous 
Tertiary 
Quaternary