By and Under

By preposition - Along the way of.

Under and by are semantically related in on topic. In some cases you can use "Under" instead a preposition "By", when it comes to topics like over, of, per.

Under adverb - In or to a lower place.

By and under are semantically related in on topic. Sometimes you can use "By" instead a preposition "Under", if it concerns topics such as over, of, per.