billion

As a noun multibillionaire is

a person with a net worth of multiple billions, typically measured in us dollars.

As a noun gigabase is

(genetics) one billion bases (nucleotides) as a unit of length of a nucleic acid.

As a noun megaproject is

a very large public investment project, especially one costing more than one billion us dollars.

As a numeral billion

is a milliard, a thousand million: 1 followed by nine zeros, 10⁹.

As a noun gigaton is

a measure of the strength of an explosion or a bomb based on how many billion tons of TNT would be needed to produce the same energy.