bil ‧ lion /ˈbɪljən/ BrE AmE number ( plural billion or billions )
[ Date: 1600-1700 ; Language: French ; Origin: bi- + -illion (as in million ) ]
1 . the number 1,000,000,000:
The final cost could be as much as one billion dollars.
two/three/four etc billion
3.5 billion years ago
Overseas debt is a staggering £16 billion.
billions of pounds/dollars etc
Airlines have lost billions of dollars.
2 . an extremely large number of things or people
a billion
A billion stars shone in the night sky.
billions of something
There are billions of things I want to say.
3 . British English old use the number 1,000,000,000,000
—billionth adjective
—billionth noun [countable]