Definition of eightieth in US English:

eightieth

ordinal number

  • 1Constituting number eighty in a sequence; 80th.

    ‘an eightieth birthday tribute’
  • 2Each of eighty equal parts into which something is or may be divided.

    ‘an eightieth of the Earth's mass’

Pronunciation

eightieth

/ˈeɪdiəθ//ˈādēəTH/