1610s, "without taste or perceptible flavor," from Middle French insipide "insipid" (16c.), from Late Latin inspidus "tasteless," from in- "not" (see in- (1)) + Latin sapidus "tasty," from sapere "have a taste" (also "be wise;" see sapient). Figurative meaning "uninteresting, dull" first recorded in English 1640s, probably from Medieval Latin or the Romance languages, where it was a secondary sense.
In ye coach ... went Mrs. Barlow, the King's mistress and mother to ye Duke of Monmouth, a browne, beautifull, bold, but insipid creature. [John Evelyn, diary, Aug. 18, 1649]Related: Insipidly.