Definitions for eoceneˈi əˌsin
Random House Webster's College Dictionary
noting or pertaining to an epoch of the Tertiary Period, occurring from 55 million to 40 million years ago, characterized by the advent of the modern mammalian orders.
(n.)the Eocene Epoch or Series.
Origin of Eocene:
Eocene, Eocene epoch(noun)
from 58 million to 40 million years ago; presence of modern mammals
the Eocene epoch
of a geologic epoch within the Paleogene period from about 56 to 34 million years ago.
pertaining to the first in time of the three subdivisions into which the Tertiary formation is divided by geologists, and alluding to the approximation in its life to that of the present era; as, Eocene deposits
the Eocene formation