1. (noun)billion, one million million, 1000000000000 the 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
2. (noun)million, billion, trillion, zillion, jillion, gazillion a very large indefinite number (usually hyperbole) "there were millions of flies"
3. (adj)billion, one thousand million, 1000000000 the number that is represented as a one followed by 9 zeros
4. (adj)billion denoting a quantity consisting of one thousandmillion items or units in the United States