Yours, Etc.: Origins and Uses of 8 Sign-Offs
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." Sense of "to introduce tortuously or indirectly" is from 1640s. Related: Insinuated; insinuating; insinuatingly.