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1. One quadrillion (1015): petahertz.
2. 1,125,899,906,842,624 (250): petabyte.
[Alteration of penta-from its representing the fifth power of a thousand).]
(Units) denoting 1015: petametres. Symbol: P
[C20: so named because it is the SI prefix after tera-; on the model of penta-, the prefix after tetra-]
a combining form used in the names of units of measure equal to one quadrillion (1015) of a given base unit.