n. & adj.
--n. (pl. same or (in sense 3) billions) (in sing. prec. by a or one)
1. a thousand million (1,000,000,000 or 10(9)).
2 (now less often, esp. Brit.) a million million (1,000,000,000,000 or 10(12)).
3 (in pl.) colloq. a very large number (billions of years).
--adj. that amount to a billion.
Derivatives:
billionth adj. & n.
Etymology: F (as BI-, MILLION)