period

Concise Oxford English Dictionary © 2008 Oxford University Press:
period/ˈpɪəriəd/

▶noun

• 1 a length or portion of time.

  ■ a major division of geological time that is a subdivision of an era and is itself subdivided into epochs.

• 2 each of the set divisions of the day in a school.

• 3 (also menstrual period) a monthly flow of blood and other material from the lining of the uterus, occurring in women of childbearing age when not pregnant.

• 4 N. Amer. a full stop.

• 5 Physics the interval of time between successive occurrences of the same state in an oscillatory or cyclic phenomenon.

• 6 Mathematics the interval between successive equal values of a periodic function.

• 7 Chemistry a set of elements occupying a horizontal row in the periodic table.

• 8 Astronomy the time taken by a celestial object to rotate about its axis, or to make one circuit of its orbit.

• 9 Rhetoric a complex sentence, especially one consisting of several clauses, constructed as part of a formal speech or oration.

▶adjective belonging to or characteristic in style of a past historical time: period furniture.

– derivatives
periodization (or periodisation) noun,
periodize (or periodise) verb.

– origin ME: from OFr. periode, via L. from Gk periodos ‘orbit, recurrence, course’.