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