1610s, "without taste or perceptible flavor," from French insipide (16c.), from Late Latin inspidus "tasteless," from Latin in- "not" (see in- (1)) + sapidus "tasty," from sapere "have a taste" (also "be wise;" see sapient). Figurative meaning "uninteresting, dull" first recorded 1640s, but it was also a secondary sense in Medieval Latin.
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.