Ληθαῖον Save Could not find Ληθαίῳ in Logeion dictionaries. Ληθαίῳ Proper-name noun: masculine dative singular of Λήθαιος Ληθαίῳ Proper-name noun: masculine dative singular of Ληθαῖος See Ληθαίῳ in Morpho Brill-Montanari Ληθαῖον πεδίον, τό Lethaian Plain, in Boeotia Thgn. 1216.