A work of art or drama which evokes a particular historical era. / A work which evokes the era in which it was produced, but may not have any other especial features.

(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.

a school period in which a student has free time, i.e., is not enrolled in a class.

(physics) Half of the period of a wave etc; typically the time taken for part of a wave to be replaced by a similar part that is out of phase.

plural of periodical comet