Augustine of Hippo

(Serm. in Mont. i. 9.) And there is this same distinction between the first case here put by the Saviour and the second: in the first case there is one thing, the passion; in the second two, anger and speech following thereupon, He who saith to his brother, Raca, is in danger of the council. Some seek the interpretation of this word in the Greek, and think that Raca means ragged, from the Greek ῥάκος, a rag. But more probably it is not a word of any meaning, but a mere sound expressing the passion of the mind, which grammarians call an interjection, such as the cry of pain, ‘heu.’