period

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An interval of time characterized by the occurrence of a certain condition, event, or phenomenon.
• noun An interval of time characterized by the prevalence of a specified culture, ideology, or technology.
• noun An interval regarded as a distinct evolutionary or developmental phase.
• noun Geology A unit of time, longer than an epoch and shorter than an era.
• noun Any of various arbitrary units of time, especially.
• noun Any of the divisions of the academic day.
• noun Sports & Games A division of the playing time of a game.
• noun Physics & Astronomy The time interval between two successive occurrences of a recurrent event or phases of an event; a cycle.
• noun A point or portion of time at which something is ended; a completion or conclusion.
• noun 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.
• noun The full pause at the end of a spoken sentence.
• noun A sentence of several carefully balanced clauses in formal writing.
• noun A metrical unit of quantitative verse consisting of two or more cola.
• noun An analogous unit or division of classical Greek or Latin prose.
• noun Music A group of two or more phrases within a composition, often made up of 8 or 16 measures and terminating with a cadence.
• noun 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.
• noun A group of digits separated by commas in a written number.
• noun The number of digits that repeat in a repeating decimal. For example, ¹/₇ = 0.142857142857 … has a six-digit period.
• noun Chemistry A sequence of elements arranged in order of increasing atomic number and forming one of the horizontal rows in the periodic table.
• adjective Of, belonging to, or representing a certain historical age or time.
• interjection Used to emphasize finality, as when expressing a decision or an opinion.

from The Century Dictionary.

• To put an end to.
• To end; cease.
• noun plural The menses.
• noun In physical, the time of one complete oscillation or cycle of a periodic motion; the reciprocal of the frequency of a periodic motion.
• noun In astronomy, the time of the revolution of a planet or satellite around its primary. Also orbital period.
• noun In geology, technically, one of the larger divisions of geologic time of either the second or the third order, measured by the time of deposition of a ‘group’ or ‘system’ of formations, and characterized by the presence of a number of allied and similar faunas which as a whole differ from those of other periods.
• noun A circuit: a round; hence, the time in which a circuit or revolution, as of a heavenly body, is made; the shortest interval of time within which any phenomenon goes through its changes of pass through them again immediately as before.
• noun Any round of time, or series of years, days, etc.
• noun An indefinite part of any continued state, existence, or series of events; an epoch: as, the first period of life; the last period of a king's reign; the period of the French revolution.
• noun The point of completion of a cycle of years or round or series of events; limit; end; conclusion; termination.
• noun Hence— The end to be attained; goal.
• noun In rhetoric, a complete sentence from one full stop to another; a passage terminated by a full pause.
• noun In ancient prosody, a group of two or more cola.
• noun In music, a definite and complete division of a composition, usually consisting of two or more contrasted or complementary phrases; a complete musical sentence.
• noun The point or character that marks the end of a complete sentence, or indicates an abbreviation, etc.; a full stop, thus(.).
• noun In math.: The smallest constant difference which, added to the value of a variable, will leave that of a function (of which it is said to be the period) unchanged.
• noun In vulgar arithmetic, one of several similar sets of figures or terms, marked by points or commas placed regularly after a certain number, as in numeration, in circulating decimals, and in the extraction of roots. Sometimes called degree.
• noun In medicine, one of the phases or epochs which are distinguishable in the course of a disease.
• noun Duration, continuance, term.
• noun Bound, determination.

from the GNU version of the Collaborative International Dictionary of English.

• noun A portion of time as limited and determined by some recurring phenomenon, as by the completion of a revolution of one of the heavenly bodies; a division of time, as a series of years, months, or days, in which something is completed, and ready to recommence and go on in the same order.
• noun A stated and recurring interval of time; more generally, an interval of time specified or left indefinite; a certain series of years, months, days, or the like; a time; a cycle; an age; an epoch.
• noun (Geol.) One of the great divisions of geological time. See the Chart of Geology.
• noun The termination or completion of a revolution, cycle, series of events, single event, or act; hence, a limit; a bound; an end; a conclusion.
• noun (Rhet.) A complete sentence, from one full stop to another; esp., a well-proportioned, harmonious sentence.
• noun (Print.) The punctuation point [.] that marks the end of a complete sentence, or of an abbreviated word.