Old English 'understandan' — 'to stand among,' where 'under' meant 'amid,' not 'beneath.'
To perceive the intended meaning of words, a language, or a speaker; to comprehend the nature or significance of something.
From Old English 'understandan' meaning 'to understand, to comprehend,' literally 'to stand among or close to,' from 'under' (among, between, in the midst of — not 'beneath' in this compound) and 'standan' (to stand). The original image was of standing in the midst of something — standing among the facts, standing close to the matter — in order to grasp its meaning. The 'under' in 'understand' does not mean 'below' but preserves an older sense of 'among, between,' also seen in German 'unter' (among) and Latin 'inter' (between, among). To understand is to stand among, not to stand beneath. Key
Every Germanic language built its word for 'understand' from 'stand' plus a preposition, but each chose a different preposition. English used 'under' (among): understandan. German used 'ver-' (before): verstehen. Swedish used 'för-' (before/for): förstå. All arrived at 'comprehension' through the metaphor of physical positioning — to understand is to stand in the right place relative to what you're trying to grasp.