billion

Concise Oxford English Dictionary © 2008 Oxford University Press:
billion/ˈbɪljən/

▶cardinal number (pl. billions or (with numeral or quantifying word) same)

• 1 the number equivalent to the product of a thousand and a million; 1,000,000,000 or 10⁹.

  ■ Brit. dated a million million (1,000,000,000,000 or 10¹²).

• 2 (billions) informal a very large number or amount.

– derivatives
billionth ordinal number.

– origin C17: from Fr., from million, by substitution of the prefix bi- ‘two’ for the initial letters.