Definition of billionth in English:

billionth

ordinal number

  • 1Constituting number one billion in a sequence; 1,000,000,000th.

    ‘the birth of India's billionth citizen’
    1. 1.1informal Constituting an unspecified but very large number in a sequence.
      ‘I was late again for the billionth time’
  • 2Each of one billion equal parts into which something is or may be divided.

    ‘particles so small they're measured in billionths of a metre’

Pronunciation

billionth

/ˈbɪlɪənθ/