1 (formal, especially BrE) = on or onto
The decision was based upon two considerations.
Although the word upon has the same meaning as on, it is usually used in more formal contexts or in phrases such as once upon a time
and row upon row of seats
Its political philosophy is utilitarian, reflecting the value put upon outcomes.
He felt his talent muffled by the perpetual eavesdropping upon his every move.
2. up and on; upward so as to get or be on:
He climbed upon his horse and rode off.
3. in an elevated position on:
There is a television antenna upon every house in the neighborhood.
4. in or into complete or approximate contact with, as an attacker or an important or pressing occasion:
The enemy was upon us and our soldiers had little time to escape.
The Christmas holiday will soon be upon us and we have hardly begun to buy gifts.
The time to take action is upon us.
5. immediately or very soon after:
She went into mourning upon her husband's death.
6. on The occasion of:
She was joyful upon seeing her child take his first steps.
7-used to emphasize that there is a large number or amount of
mile upon mile of dusty road
mile upon mile of golden sand
thousands upon thousands of lettershttp://www.ldoceonline.com/dictionary/uponhttp://oxforddictionaries.com/definition/english/uponhttp://dictionary.reference.com/browse/upon