late 14c., "contemptuous, arrogant, haughty," from Latin insolentem (nominative insolens) "arrogant, immoderate," literally "unusual," from in- "not, opposite of" (see in-(1)) + solentem, present participle of solere "be accustomed," which possibly is related to sodalis "close companion," and to suescere "become used to." Meaning "contemptuous of rightful authority" is from 1670s. Related: Insolently.