Definition of quadrillionth in US English:

quadrillionth

ordinal number

  • See quadrillion

    • ‘With the neutrons traveling much, much faster, I estimate about 28 percent of the material will go critical in that quadrillionth of a second.’
    • ‘A femtosecond is a millionth of a billionth (or one quadrillionth) of a second.’
    • ‘In addition, LCLS X-ray pulses will be extremely short - lasting only femtoseconds, mere quadrillionths of a second.’

Pronunciation

quadrillionth

/-ˈdrilyənT͟H/