Raca is a word that comes from the Aramaic term reqa. It was a derogatory expression meaning empty-headed.
1 If you called someone Raca you were insinuating that they are stupid and inferior to you. As such, it is an offensive name used to show contempt for another person.
22 Mais moi, je vous dis que quiconque se met en colère contre son frère est passible de jugement; que celui qui dira à son frère: Raca! mérite d'être puni par le sanhédrin; et que celui qui lui dira: Insensé! mérite d'être puni par le feu de la géhenne.