[ 'i:ə(ʊ)si:n ]
■ adjective Geology relating to or denoting the second epoch of the Tertiary period (between the Palaeocene and Oligocene epochs, 56.5 to 35.4 million years ago), a time when the first horses, bats, and whales appeared.
Origin
C19: from Gk ēōs 'dawn' + kainos 'new'.