Alternative forms 
From Middle English upon, uppon, uppen, from Old English upon, uppon, uppan (“on, upon, up to, against, after, in addition to”), equivalent to up (“adverb”) + on (“preposition”). Cognate with Icelandic up á, upp á (“up on, upon”), Swedish på (“up on, upon”).
- Being above and in contact with another.
- Place the book upon the table.
- Being directly supported by another.
- The crew set sail upon the sea.
- She balanced upon one foot.
- At a prescribed point in time.
- The contract was rendered void upon his death.
Usage notes 
A somewhat elevated word; the simpler, more general term on is generally interchangeable, and more common in casual American speech. In poetic or legal contexts, upon is common.
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upon (not comparable)
- Being the target of an action.
- He was set upon by the agitated dogs
- Incidental to a specified point in time or order of action; usually combined with here-, there- or where-.
- The clock struck noon, whereupon the students proceeded to lunch.