“Cattywampus” (1834) has held a variety of meanings and spellings, including as an adverb (catawampusly) meaning “completely/utterly/avidly,” a name for a fantastical imp-like creature or a mountain lion, and an adjective meaning “askew,” from obsolete “cater,” from the Greek prefix kata- (downward, toward), and perhaps from the old Scottish slang wampish (to wriggle or twist about.)
The word “cattywampus,” has also been spelled in a variety of other ways including catawampus, catiwampus, etc.
When it was first used in the U.S. around 1834 as an adverb, it meant “completely, utterly or avidly.”
It first appeared as a noun (catawampus) in Dickens’ Martin Chuzzlewit (1843), though it probably was first recorded as a noun in American works shortly before that. In that sense, it suggested some sort of hobgoblin or other frightening fantastical creature, likely influenced by “catamount,” another word for a cougar or other large cat (shortened from “catamountain,” or “cat of the mountain”). This is the passage in which it appears:
‘Am I rightly informed,’ he says; not exactly though his nose, but as if he’d got a stoppage in it, very high up: ‘that you’re a-going to the Walley of Eden?’ ‘I heard some talk on it,’ I told him. ‘Oh!’ says he, ‘if you should ever happen to go to bed there—you may you know,’ he says, ‘in course of time as civilization progresses—don’t forget to take a axe with you.’ I looks at him tolerable hard. ‘Fleas?’ says I. ‘And more,’ says he. ‘Wampires?’ says I. ‘And more,’ says he. ‘Musquitoes, perhaps,’ says I. ‘And more,’ says he. ‘What more?’ says I. “Snakes more,’ says he; ‘rattlesnakes. You’re right to a certain extent stranger. There air some catawampous chawers in the small way too, as graze upon a human pretty strong; but don’t mind them, they’re company. It’s snakes,’ he says, ‘as you’ll object to: and whenever you wake and see one in a upright poster on your bed,’ he says, ‘like a corkscrew with the handle off a-sittin’ on s bottom ring, cut him down, for he means wenom.’
More in line with its current meaning, the first part, “catty,” may hark back to a now-obsolete meaning of the word “cater,” which means “to set or move diagonally” (in the sense of catty-corner, which was originally “cater-corner” and perhaps changed spelling as a result of developments in American accents). The first part might also be related to the Greek prefix kata-, which can suggest “downward” or “toward,” among other meanings.
The second part’s origin is unclear, but may be from the Scottish slang term wampish, which meant “to wriggle or twist about.”
Through the 1840s, it was used in other British works to tease at American slang (particularly colloquialisms from North Carolina), and by 1864, it had fully adopted its current sense (and lack of consistent spelling), i.e., “askew or awry.” By 1873, it commonly meant “in a diagonal position, on a bias, or crooked.”
Useless Etymology 