(music) the musical period of time following the Baroque period and preceding the Romantic period, spanning c.1750-c.1820.

plural of periodic function

(historical) The history of Japan covering the years from AD 710 to 794. Empress Gemmei established the capital of Heijō-kyō (present-day Nara).

Sexual intercourse during menstruation.

(education) A high school class that is offered early in the morning, before the scheduled start of the school day.

(astronomy) The apparent orbital period of a planet as seen from Earth.

(astronomy) sidereal orbital period / (astronomy) sidereal rotation period

(history) The age of mass migration of Germanic people in Europe during the early Middle Ages, circa 376 to 800 AD.

(astronomy) Taking over 200 years to complete an orbit; especially said of comets.

Any of certain species of cicadas, especially in genus Magicicada, which are known for their 17- and 13-year life-cycles, during most of which they develop underground, emerging in large numbers for a short time as large and audible adults, all those emerging in a year constituting a brood.