from Wiktionary, Creative Commons Attribution/Share-Alike License
- proper n. A classical Greek mathematician, living circa 417–369 B.C., credited with proving that there are precisely five regular convex polyhedra.
- proper n. A later middle dialogue of Plato concerning epistemology.
- proper n. A lunar impact crater 2·8 kilometres in depth and 25 kilometres in diameter, located southeast of the crater Cassini, near the eastern edge of Mare Imbrium, at coördinates 37·0° N, 6·0° E.
From Ancient Greek Θεαίτητος (Theaitētos); the mathematician is the eponym of the dialogue and the lunar crater. (Wiktionary)