Low and Under

Low adjective - Of, relating to, or located at the bottom.

Under is a synonym for low in short topic. In some cases you can use "Under" instead the word "Low" as an adjective or an adverb, when it comes to topics like over.

Under adjective - Located below or beneath something else.

Low is a synonym for under in over topic. You can use "Low" instead the word "Under" as an adjective or an adverb, if it concerns topics such as secondary.