billionth

WordReference Random House Learner's Dictionary of American English © 2026

bil•lion /ˈbɪlyən/   n. [countable] , pl. -lions, [or, after a number] -lion, adj. 
n. 

1. a cardinal number represented by 1 followed by 9 zeros:
   the sum of two billion dollars.
2. any vaguely large number:
   I've told you a billion times.
3. (formerly, in Great Britain) a cardinal number represented by 1 followed by 12 zeros.

adj. [before a noun]

4. equal in number to a billion:
   a billion-dollar industry.

bil•lionth, adj., n. [countable]
Usage

See hundred.

WordReference Random House Unabridged Dictionary of American English © 2026

bil•lion  (bil′yən), n., pl. -lions, (as after a numeral) -lion, adj. 
n. 

1. a cardinal number represented by 1 followed by 9 zeros.
2. a very large number:
   I've told you so billions of times.
3. (formerly, in Great Britain) a cardinal number represented by 1 followed by 12 zeros.

adj. 

4. equal in number to a billion.

• French, equivalent. to b(i)- bi-¹ + -illion, as in million
• 1680–90

bil′lionth, adj., n.