upo
“under, up from below, over”over/up
PIE preposition meaning under, up from below, or over. Source of Latin sub/super, English "up," Greek hypo/hyper.
Discussion
*upo is a Proto-Indo-European preposition meaning "under," "up from below," or "over," with a remarkable semantic range spanning vertical space.
Latin sub "under" (whence English sub-, submarine, subtract, subject, substance, suburb) and super "over, above" (whence English super-, supreme, sovereign) both derive from this root with different suffixation. Greek hypó "under" (whence hypo-, hypothesis, hypodermic) and hypér "over" (whence hyper-, hyperbole, hyperactive) show the same dual development.
Old English up (modern English up, upon, upper) and ofer "over" (modern English over) reflect the Germanic branch, where both the "upward" and "over" senses survive. German über "over" and auf "up, on" continue the pattern.
Sanskrit úpa "near, toward, under" preserves the Indo-Iranian form. The apparent contradiction between "under" and "over" resolves when the original sense is understood as "at the base of and moving upward"—beneath something but oriented toward its top.
Modern descendants include English up, upper, over, and through Latin/Greek: sub-, super-, hypo-, hyper-, submarine, supreme, sovereign, hypothesis, and hyperbole.
Notes
Source of Latin "sub" (under), English "up", "over". Ambiguous vertical axis.