upon
/əˈpɒn/preposition
- more formal term for on, especially in abstract senses〈正式〉同ON（尤用于抽象意义）：
it was based upon two principles.
它以两个原则为根据。
a school's dependence upon parental support.
学校对家长支持的依赖。
USAGE
the preposition upon has the same core meaning as the preposition on. However, in modern English upon tends to be restricted to more formal contexts or to established phrases and idioms, as in once upon a time and row upon row of seats.
词源