1520s, from Latin insinuatus, past participle of insinuare "to throw in, push in, make a way; creep in, intrude, bring in by windings and curvings, wind one's way into," from in- "in" (see in-(2)) + sinuare "to wind, bend, curve," from sinus "a curve, winding" (see sinus). Sense of "to introduce tortuously or indirectly" is from 1640s. Related: Insinuated; insinuating; insinuatingly.