μέγας ῥεῖν

From LSJ

ἐγώ εἰμι τὸ φῶς τοῦ κόσμου· ὁ ἀκολουθῶν μοι οὐ μὴ περιπατήσῃ ἐν τῇ σκοτίᾳ ἀλλ' ἕξει τὸ φῶς τῆς ζωῆς → I am the light of the world; he that followeth me shall not walk in darkness but shall have the light of life (John 8:12)

Source

Greek > English (Woodhouse)

be in full flood, flow with a strong stream