upon

US /əˈpɑːn/
UK /əˈpɑːn/
"upon" picture
1.

more formal term for on, especially in abstract senses

:
The decision was based upon careful consideration.
He placed the book upon the table.
2.

indicating a time immediately or very soon after something

:
Upon arrival, please report to the front desk.
He started crying upon hearing the news.