The story
Coined by Thomas Henry Huxley in 1872 as hypo- + plastron. Superseded the earlier hyposternum, a nominalised form of the French adjective hyposternal, coined by Étienne Geoffroy Saint-Hilaire in 1818. The prefix is from Ancient Greek ὑπό (hupó, “under”), in reference to its position in the posterior portion of the plastron.
Etymology from Wiktionary, CC BY-SA 4.0.