n.
the SI units of time, equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom. This unit is now the basis of all time measurements. Symbol: s.
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sec·ond (s) (sekґənd) the SI unit of time, equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium 133.Medical dictionary. 2011.