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ἐπειδὴ

Μὴ φῦναι τὸν ἅπαντα νικᾷ λόγον -> Not to be born is, past all prizing, best.
Sophocles, Oedipus Coloneus l. 1225

Greek (Liddell-Scott)

ἐπειδὴ: ἢ ἐπεὶ δὴ (ὡς γράφεται νῦν παρ’ Ὁμ.) ἐντονώτερος τύπος τοῦ ἐπεὶ, ἴδε ἐν λ. ἐπεί.