Mi·o·cene 
(mīə-sēn′)
(mīə-sēn′)adj.
Of, relating to, or being the epoch of geologic time from about 23 to 5.3 million years ago, the fourth epoch of the Tertiary Period. It is characterized by the spread of grasses and grazing mammals. See Table at geologic time.
n.
The Miocene Epoch.
[Greek meiōn, less; see mei-2 in the Appendix of Indo-European roots + -CENE.]