The word "upon" is a preposition used to indicate a position or situation that refers to being in contact with, or supported by, a surface or object. It is often used in a more formal or literary context, meaning "on" or "at" and can imply carrying out an action in relation to something else.
The word "upon" originates from Middle English "up on," which combines "up" (higher position) with the preposition "on." Its roots can be traced back to Old English "uppan," composed of "upp-" meaning "up" and the suffix "-an," which is a preposition.