(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.

(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 sunrise period

plural of periodic structure

Alternative form of Question Period

(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

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

(music) the musical period of time following the Classical period falling between about 1820 and the start of the twentieth century.

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