(politics, government) In Canadian federal and provincial parliaments, a period of regularly scheduled time in the lower chamber during which members of the official opposition party and other members may direct questions to the prime minister and to cabinet ministers concerning affairs of state.

(chemistry) The principle that chemical properties of the elements are periodic functions of their atomic numbers

(Internet) The period of time at the launch of a new top-level domain or second-level domain during which trademark owners may register domain names containing their trademarks (to prevent cybersquatting).

plural of periodic structure

(Britain, informal, plural only) Underwear worn by a woman or girl during menstruation, typically old, cheap, or of a dark colour in case of staining.

(grammar) A sentence whose main clause appears at the end, after other, especially dependent, clauses. / (physics) A structure made of bays coupled through one or more coordinates.

(biology) The period, after excitation, during which a membrane recovers its polarization and is not able to respond to a second stimulus.

a work of the screen that evokes a particular historical period

(astronomy) The roughly 1460-year period of time between successive alignments of the first days of the Egyptian civil calendar and the observational Sothic year.

(psychology, biology) A maturational stage in the lifespan of an organism during which the nervous system is especially sensitive to certain environmental stimuli.