celerissimus

From LSJ

ἔξαψις σφοδρὰ μετὰ πολλῆς βίας πίπτουσα ἐπὶ γῆς → a violent flare-up falling on the ground with great force, thunder and lightning

Source

Latin > French (Gaffiot 2016)

cĕlĕrissimus, v. celer.