δοῖεν

From LSJ

οὗτος μὲν ὁ πιθανώτερος τῶν λόγων εἴρηται, δεῖ δὲ καὶ τὸν ἧσσον πιθανόν, ἐπεί γε δὴ λέγεται, ῥηθῆναι → this is the most credible of the stories told; but I must relate the less credible tale also, since they tell it

Source

French (Bailly abrégé)

3ᵉ pl. opt. ao.2 de δίδωμι.

Russian (Dvoretsky)

δοῖεν: 3 л. pl. aor. 2 opt. к δίδωμι.