(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.

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.

a work of the screen that evokes a particular historical period

plural of Sothic 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.