(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.

plural of periodic structure

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

plural of periodic function

Sexual intercourse during menstruation.

plural of sunrise period

(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.

(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