Earlier (1676) nicompoop, possibly from Latin non compos mentis (“not of sound mind”), although the lack of the second n in the early form casts doubt on this origin. The earliest known use of the nincompoop spelling is from 1680.
nincompoop (plural nincompoops)
- A silly or foolish person.
- 1680, Matthew Stevenson, The wits paraphras'd: or, Paraphrase upon paraphrase: In a burlesque on the several late translations of Ovids Epistles ..., page 161:
- Tis such another Nincompoop,
I sleep, and he begins to droop.
He sees, yet keeps his Eyes a winking,
Says nought, but pays it off with thinking.
- 1694, Thomas D'Urfey, “Part I, Act I, Scene I”, in The Comical History of Don Quixote: As it was Acted at the Queen's Theatre in Dorset-Garden ..., page 6:
- ...Heaven knows the time when? Art not thou asham’d to see me, thou Nincompoop?
- 1905, Baroness Emmuska Orczy, The Scarlet Pimpernel 
- No wonder that Chauvelin's spies had failed to detect, in the apparently brainless nincompoop, the man whose reckless daring and resourceful ingenuity had baffled the keenest French spies...