εὐδίοπτον

From LSJ

ὁδὸς ἄνω κάτω μία καὶ ὡυτή → the road up and the road down is one and the same, the upward path and the downward path are the same

Source

Russian (Dvoretsky)

εὐδίοπτον: τό прозрачность (τῆς θαλάττης Arst.).