1560s, "triumph over in an arrogant way" (obsolete), from Middle French insulter "to wrong; reproach; triumph arrogantly over," earlier "to leap upon" (14c.) and directly from Latin insultare "to assail, to make a sudden leap upon," which was used by the time of Cicero in sense of "to insult, scoff at, revile," frequentative of insilire "leap at or upon," from in- "on, at" (from PIE root *en "in") + salire "to leap" (see salient (adj.)).
Sense of "verbally abuse, affront, assail with disrespect, offer an indignity to" is from 1610s. Related: Insulted; insulting.