**Quad*ril"lion** (?), n. [F., fr. L. *quater* four times, akin to *quattuor* four, E. *four*; -- formed like *million*. See Four, Million.]

According to the French notation, which is followed also upon the Continent and in the United States, a unit with fifteen ciphers annexed; according to the English notation, the number produced by involving a million to the fourth power, or the number represented by a unit with twenty-four ciphers annexed. See the Note under Numeration.

© Webster 1913.