Nouns

(n)billion, one million million, 1000000000000the number that is represented as a one followed by 12 zeros; in the United Kingdom the usage followed in the United States is frequently seen
(n)million, billion, trillion, zillion, jillion, gazillion, bazilliona very large indefinite number (usually hyperbole)“there were millions of flies”
(n)billion, one thousand million, 1000000000the number that is represented as a one followed by 9 zeros

Adjectives

(s)billiondenoting a quantity consisting of one thousand million items or units in the United States
(s)billiondenoting a quantity consisting of one million million items or units in Great Britain