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εἰδῶ

Γελᾷ δ' ὁ μωρός, κἄν τι μὴ γέλοιον ᾖ -> The fool laughs even when there's nothing to laugh at
Menander

French (Bailly abrégé)

ῇς, ῇ;
sbj. de οἶδα, pf.2 de *εἴδω.

Russian (Dvoretsky)

εἰδῶ: эп. εἰδέω pf. conjct. к *εἴδω.