n. 1. a. A unit of time equal to one sixtieth of a minute. b. The time needed for a cesium-133 atom to perform 9,192,631,770 complete oscillations. See Table at measurement. 2. A brief interval of time; a moment. See Synonyms at moment. 3. Mathematics A unit of angular measure equal to one sixtieth of a minute. In this sense, also called arcsecond, second of arc. [Middle English seconde, from Old French, from Medieval Latin (pars minūta) secunda, second (small part), feminine of Latin secundus, second, following; see SECOND2.] |
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