Miocene
Concise Oxford English Dictionary © 2008 Oxford University Press:
Miocene /ˈmʌɪə(ʊ)siːn/
▶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’.
'Miocene' also found in these Oxford entries:

