ETYM French billion, arbitrarily formed from Latin bis twice, in imitation of million a million. Related to Million.
A thousand millions. The cardinal number represented by a 1 followed by nine zeros (1,000,000,000 or 109), equivalent to a thousand million.
1. (In Britain) The number that is represented as a one followed by 12 zeros; SYN. one million million, 1000000000000.
2. (In the United States) The number that is represented as a one followed by 9 zeros; SYN. one thousand million, 1000000000.

(U.S.) Denoting a quantity consisting of one thousand million items or units; (Britain) denoting a quantity consisting of one million million items or units; SYN. a billion.
1. In American usage (as is usual with microcomputers), a thousand million, or 109. Computer terminology uses the prefixes giga- for 1 billion and nano- for 1 billionth.
2. In British usage, a million million, or 1012, which is a trillion in American usage.