A number equal to 1 followed by 15 zeroes; 10^15.
Late 18th century: from french, from quadri- (from latin quattuor "four") + -illion (from million).
- It's hard to imagine a quadrillion of anything.
- The national debt is measured in trillions, not quadrillions.
- The number of stars in the universe is estimated to be around 10^22, or one sextillion.
- A quadrillion dollars is an enormous amount of money.
- The number of atoms in a mole of a substance is Avogadro's number, which is 6.022 x 10^23, or six sextillion.