The story
Coined by Thomas Henry Huxley in 1872 as epi- + plastron. Superseded the earlier episternum, a nominalised form of the French adjective épisternal, coined by Étienne Geoffroy Saint-Hilaire in 1818. The prefix is from Ancient Greek ἐπί (epí, “on top of”), in reference to its position as the anteriormost bone of the plastron.
Etymology from Wiktionary, CC BY-SA 4.0.