upon

/əˈpɑn/
preposition
  1. On; used to show that something is in a position above and touching something else.
    • The cat jumped upon the windowsill.
    • She placed the book upon the table.
    • He rested his head upon the pillow.
  2. Immediately after or as a result of something.
    • The meeting ended upon the arrival of the CEO.
    • Upon hearing the news, she burst into tears.
    • Upon finishing the race, he collapsed from exhaustion.
  3. Used to indicate a particular time or occasion.
    • Upon my arrival, I was greeted warmly.
    • The contract was signed upon the first day of the month.
    • Upon reflection, I realized I had made a mistake.
Synonyms
What does "upon" mean? | whatsthatwordmean | whatsthatwordmean