It's an older version of "under" I guess. The weird thing is that the word "substance" has such a similar looking construction, because it literally means that which stands beneath.
English in general uses a lot of seemingly random direction words in phrases, like "party down", "man up", "buckle up", etc.
Which comes to English from Old English and its Germanic origins. 'Unter' and 'Standen' are the Germanic equivalents today, signifying the original intent, to stand together on something.
'Comprehend' from the Normans' French (and Latin before that) is much easier to grok für Ausländer in this case.
It's an older version of "under" I guess. The weird thing is that the word "substance" has such a similar looking construction, because it literally means that which stands beneath.
English in general uses a lot of seemingly random direction words in phrases, like "party down", "man up", "buckle up", etc.