Green’s Dictionary of Slang

an absurd person.

1790		Bystander 93: Mr. World [i.e. the newspaper] might retort that Mr. Herald was a Quoz, and a low prin.
1795		Sporting Mag. Mar. V 324/2: Such was precisely the origin of the word Quoz, which some few years ago was an object of so much ridiculous speculation; a word of no meaning whatsoever, but which was considered by the sagacious many as of deep import!
1841		C. Mackay Memoirs of Extraordinary Popular Delusions 325: Many years ago the favourite phrase (for, though but a monosyllable, it was a phrase in itself) was quoz. This odd word took the fancy of the multitude in an extraordinary degree, and very soon acquired an almost boundless meaning.