Nincompoop

Earlier (1676) nicompoop, from Latin non compos mentis ("not of sound mind"). The earliest known use of nincompoop spelling is from 1680.

Full definition of nincompoop

(plural nincompoops)

1680, Matthew Stevenson, The wits paraphras'd: or, Paraphrase upon paraphrase: In a burlesque on the several late translations of Ovids Epistles ..., 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, The Comical History of Don Quixote: As it was Acted at the Queen's Theatre in Dorset-Garden ... Chapter Part I, Act I, Scene I, ...Heaven knows the time when? Art not thou ashamâ€™d to see me, thou Nincompoop?
1905: Baroness Emmuska Orczy, The Scarlet Pimpernel http://etext.lib.virginia.edu/etcbin/ot2www-pubeng?specfile=/texts/english/modeng/publicsearch/modengpub.o2w&act=surround&offset=507211157&tag=Orczy,+Baroness:+The+Scarlet+Pimpernel,+1905&query=+nincompoop&id=OrcPimpNo 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...