Origin: 1275–1325; Middle English bilooghe, equivalent to bi- by (see be-) + looghelow1
Synonyms 11.Below,under,beneath indicate position in some way lower than something else. Below implies being in a lower plane: below the horizon, the water line. Under implies being lower in a perpendicular line: The book is under the chair. Beneath may have a meaning similar to below, but more usually denotes being under so as to be covered, overhung, or overtopped: the pool beneath the falls.
early 14c., biloogh, from be- "by" + logh, lou, lowe "low." Apparently a variant of earlier a-lowe (influenced by other advs. in be-, cf. before), the parallel form to an-high (now on high). Beneath was the usual word; below was very rare in M.E. and only gained currency
in 16c. It is frequent in Shakespeare. Below is the opposite of above and concerns difference of level and suggests comparison of independent things. Under is the opposite of over and is concerned with superposition and subjection and suggests some interrelation.