[ 'mʌɪə(ʊ)si:n ]
■ adjective Geology relating to or denoting the fourth epoch of the Tertiary period (between the Oligocene and Pliocene epochs, 23.3 to 5.2 million years ago), a time when the first apes appeared.
Origin
C19: formed irregularly from Gk meiōn 'less' + kainos 'new'.