Aboon, and Other Prepositions You’ve Never Heard

: above

Aboon is a preposition as well as an adverb and an adjective—just like its far more common synonym above. Aboon comes from a word that resembles above as well: Middle English aboven (which also existed in the form abuven). Aboon has been in use since the beginning of the 17th century, but has never been widely used.

Marsh End had belonged to the Rivers ever since it was a house: and it was, she affirmed, 'aboon two hundred year old—for all it looked but a small, humble place, naught to compare wi' Mr. Oliver's grand hall down i' Morton Vale.
— Charlotte Brontë, Jane Eyre, 1846

: nevertheless, notwithstanding

You can spell it natheless or nathless. It's been in use (in various forms) for almost a thousand years, and comes from the Old English phrase nā thē lǣs, meaning "not the less."

Natheless, while such and so preposterous were the opinions on either side, there were, it cannot be doubted, men of virtue and worth on both, to entitle either party to claim merit from its martyrs.
— Walter Scott, The Heart of Mid-Lothian, 1818

: about, concerning

Anent is also an old word, born of ancient linguistic parentage—the Old English on efen, meaning "alongside." For more than three centuries, anent proved its usefulness, but by the 17th century its hoary syllables had gone nearly extinct. Its fate didn't end there, though: the word was revived in the 19th century and has continued to enjoy occasional use since then.

Mr Bloom and Stephen entered the cabman's shelter, an unpretentious wooden structure, where, prior to then, he had rarely if ever been before, the former having previously whispered to the latter a few hints anent the keeper of it said to be the once famous Skin-the-Goat Fitzharris, the invincible, though he could not vouch for the actual facts which quite possibly there was not one vestige of truth in.
— James Joyce, Ulysses, 1922

: despite

Malgré is the less common sibling to maugre, which shares its meaning. Maugre is older, having been borrowed into Middle English from the Anglo-French malgré way back in the 13th century. French hung on to that l in the centuries after that borrowing, and English borrowed malgré in the 17th century. The ultimate origin of both words is mal or mau, meaning "evil," and gré, meaning "grace, favor."

I was rejoiced to find myself again in London. I went to my father's house in Grosvenor-square. All the family, viz. he and my mother, were down at H--t--d; and, malgre my aversion to the country, I thought I might venture as far as Lady S--'s for a couple of days.
— Edward Bulwer-Lytton, Pelham, 1828

: out of (something, such as an agreement, record, or will) : foreign to

Dehors is one of many words borrowed from Anglo-French, that version of French that was spoken in Medieval England as a result of the Norman Conquest of 1066. Anglo-French dominated the language of literature, law, and administration in England for two centuries. Dehors has remained in the second of those realms: it's a law term.

The Court had stressed that petitioner's claim rested on facts dehors the record.
— Wayne R. LaFave & Jerold H. Israel, Criminal Procedure, (1984)1985

The term en dehors is used in ballet as both an adjective and an adverb. It means "outward," and is used of a circular ballet movement of arms or legs leading away from the body, or of the position in which the toes are turned out.

1 a : past b : near 2 : besides

Forby was a well-established preposition by the time Ralph Robynson used it in his 1551 translation of Thomas More's Utopia, which was written in Latin. Forby dates to the 14th century and comes from fore-, meaning "before," and by.

There goeth a bridge over the river made not of piles of timber, but of stonework with gorgeous and substantial arches at that part of the city that is farthest from the sea: to the intent that ships may go along forby all the side of the city without let.
— Thomas More, Utopia, 1516 (translation by Ralph Robynson, 1551)

In Scottish English, forby is also an adverb meaning "besides" or "in addition":

There are the bairns forby, the children and the hope of Appin, that must be learned their letters and how to hold a sword, in that far country.
— Robert Louis Stevenson, Kidnapped, 1886