Definition of Eocene in US English:



  • 1Relating to or denoting the second epoch of the Tertiary period, between the Paleocene and Oligocene epochs.

    The Eocene epoch lasted from 56.5 million to 35.4 million years ago. It was a time of rising temperatures, and there was an abundance of mammals, including the first horses, bats, and whales

    • ‘It includes the Palaeocene, Eocene, and Oligocene epochs, spanning the time from the end of the Mesozoic to the beginning of the Neogene.’
    • ‘Western Ecuador consists of a complex tectonic melange of oceanic terranes accreted to the continental margin from Late Cretaceous to Eocene time.’
    • ‘The La Meseta Formation is the best exposed and most fossiliferous rock unit of Eocene age in Antarctica.’
    • ‘An early Cretaceous to late Eocene volcanic arc was located in the present-day Central Depression.’
    • ‘This age is notable because it is precisely the age of the boundary between the Paleocene and Eocene epochs.’
    1. 1.1as noun the Eocene The Eocene epoch or the system of rocks deposited during it.


Mid 19th century: from Greek ēōs ‘dawn’ + kainos ‘new’.