billion

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The cardinal number equal to 10⁹.
2. n. Chiefly British The cardinal number equal to 10¹².
3. n. An indefinitely large number.

Century Dictionary and Cyclopedia

1. n. In Great Britain, a million of millions; as many millions as there are units in a million (1,000,000,000,000).
2. n. In France and the United States, a thousand millions (1,000,000,000). [The word billion was introduced into French in the sixteenth century, in the sense of a million to the second power, as a trillion was a million to the third power. At that time numbers were usually pointed off in periods of six figures. In the seventeenth century the custom prevailed of pointing off numbers in periods of three, and this led to the change in the meaning of the word billion in French. The words billion, trillion, etc., did not apparently come into use in English until a later date, for Locke (“Essay on the Human Understanding,” ii. 16, § 6, 1690) speaks of the use of billion as a novelty. The English meaning of the word is thus the original and most systematic. The word billion is not used in the French of every-day life, one thousand millions being called a milliard.]

Wiktionary

1. n. US A milliard, a thousand million: 1 followed by nine zeros, 109.
2. n. obsolete A million million: a 1 followed by twelve zeros, 1012.
3. n. colloquial, plural, hyperbolic A very large number.

GNU Webster's 1913

1. n. According to the French and American method of numeration, a thousand millions, or 1,000,000,000; according to the English method, a million millions, or 1,000,000,000,000. See numeration.

WordNet 3.0

1. n. the number that is represented as a one followed by 9 zeros
2. adj. denoting a quantity consisting of one million million items or units in Great Britain
3. n. a very large indefinite number (usually hyperbole)
4. adj. denoting a quantity consisting of one thousand million items or units in the United States
5. n. 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