https://www.etymonline.com/word/understand https://www.etymonline.com/word/understand It's an older version of "under" I guess. The weird thing is that the wo

https://www.etymonline.com/word/understand https://www.etymonline.com/word/understand 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.