(astronomy) A comet which orbits the Sun and which returns to the innermost point of its orbit at known, regular intervals.

(rhetoric) A sentence whose main clause appears at its end.

(of an astronomic object) The time taken to rotate about its axis relative to the background stars.

rotational period

A relatively brief period when a new leader is given greater leeway with respect to changes he or she wishes to make.

A period during which a new employee is monitored to assess his/her capability.

plural of period piece

(epidemiology) The time elapsed between an exposure to a pathogenic organism, a chemical or radiation, and the appearance of signs and symptoms.

An event of a woman's discharging of menstrual flow of blood and cells.

Alternative form of menstrual period