From the scholia to Homer, Iliad 15.704-5, where the headword phrase occurs (web address 1). Cf. also Homer, Odyssey 12.182, 15.473; Sophocles, Ajax 710; Moschus 2.60. Similarly glossed in Ps.-Herodian, Hesychius, and the Ambrosian Lexicon.
Although the adjective ὠκύαλος strictly means "sea-swift, speeding over the sea" (LSJ s.v., web address 2), later writers could apply it to swiftness or violence in other contexts: so Oppian, Halieutica 2.535, and already Pindar, Parthenia 2.19.