1. An interval of time characterized by the occurrence of a certain condition, event, or phenomenon: a period of economic prosperity.
2. An interval of time characterized by the prevalence of a specified culture, ideology, or technology: artifacts of the pre-Columbian period.
3. An interval regarded as a distinct evolutionary or developmental phase: Picasso's early career is divided into his blue period and rose period.
4. Geology A unit of time, longer than an epoch and shorter than an era.
5. Any of various arbitrary units of time, especially:
a. Any of the divisions of the academic day.
b. Sports & Games A division of the playing time of a game.
6. Physics & Astronomy The time interval between two successive occurrences of a recurrent event or phases of an event; a cycle: the period of a satellite's orbit.
7. See menstrual period.
8. A point or portion of time at which something is ended; a completion or conclusion.
9. A punctuation mark ( . ) indicating a full stop, placed at the end of declarative sentences and other statements thought to be complete, and after many abbreviations.
10. The full pause at the end of a spoken sentence.
11. A sentence of several carefully balanced clauses in formal writing.
a. A metrical unit of quantitative verse consisting of two or more cola.
b. An analogous unit or division of classical Greek or Latin prose.
13. Music A group of two or more phrases within a composition, often made up of 8 or 16 measures and terminating with a cadence.
a. The least interval in the range of the independent variable of a periodic function of a real variable in which all possible values of the dependent variable are assumed.
b. A group of digits separated by commas in a written number.
c. The number of digits that repeat in a repeating decimal. For example, 1/7 = 0.142857142857 ... has a six-digit period.
15. Chemistry A sequence of elements arranged in order of increasing atomic number and forming one of the horizontal rows in the periodic table.
Of, belonging to, or representing a certain historical age or time: a period piece; period furniture.
Used to emphasize finality, as when expressing a decision or an opinion: You're not going to the movies tonight, period!
[Middle English periode, from Old French, from Medieval Latin periodus, from Latin perihodos, rhetorical period, from Greek periodos, circuit : peri-, peri- + hodos, way.]
Word History: Many may have wondered why the word period has the sense "punctuation mark ( . )" as well as several senses having to do with time. The answer to this question lies in one of the senses of the Greek word periodos from which our word is descended. Periodos, made up of peri-, "around," and hodos, "way," in addition to meaning such things as "going around, way around, going around in a circle, circuit," and with regard to time, "cycle or period of time," referred in rhetoric to "a group of words organically related in grammar and sense." The Greek word was adopted into Latin as perihodos, which in the Medieval Latin period acquired a new sense related to its use in rhetoric, "a punctuation mark used at the end of a rhetorical period." This sense is not recorded in English until the late 1500s, but the word had already entered Middle English in the 1400s as a borrowing from Old French in the sense "a cycle of recurrence of a disease."
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.