A triple compound from Old English 'abufan' (on-by-over), whose PIE root *upo paradoxically also means 'under.'
In or to a higher position than; over; at a greater height than.
From Old English 'abufan,' a compound of 'a-' (on) + 'bufan' (above), where 'bufan' itself is from 'be-' (by) + 'ufan' (over, above). The element 'ufan' descends from Proto-Germanic *ubana, from PIE *upo meaning 'under, up from under, over.' The same PIE root produced Latin 'sub' (under), Greek 'hypo' (under), and Sanskrit 'upa' (near, toward) — a root whose meanings oscillate between 'under' and 'over,' reflecting a sense of 'movement
The PIE root *upo is one of linguistics' great paradoxes: it means both 'under' and 'over.' Latin took the 'under' sense (sub-marine, sub-way), Greek took the 'under' sense (hypo-dermic, hypo-thesis), but Germanic took the 'up/over' sense (above, over, up). The original meaning was probably directional — 'from below upward' — which could be interpreted from either end