Pleiocene

UK: /ˈplaɪəʊˌsiːn/

Collins Concise English Dictionary © HarperCollins Publishers::

Pleiocene / ˈplaɪəʊˌsiːn/ adjective , noun

1. a variant spelling of Pliocene

WordReference Random House Unabridged Dictionary of American English © 2025

Pli•o•cene  (plī′ə sēn′), [Geol.]
adj. 

1. Geology noting or pertaining to an epoch of the Tertiary Period, occurring from 10 to 2 million years ago, and characterized by increased size and numbers of mammals, by the growth of mountains, and by global climatic cooling. See table under geologic time. 

n. 

2. Geology the Pliocene Epoch or Series.

• plio- + -cene 1825–35

Collins Concise English Dictionary © HarperCollins Publishers::

Pliocene, Pleiocene / ˈplaɪəʊˌsiːn/ adjective

1. of, denoting, or formed in the last epoch of the Tertiary period, which lasted for three million years, during which many modern mammals appeared

noun

1. the Pliocene ⇒ the Pliocene epoch or rock series

Etymology: 19th Century: plio- + -cene, from Greek kainos recent