upon Look up upon at Dictionary.com
early 12c., from up + on; probably influenced by Old Norse upp a. Distinct from Old English uppan which merely meant "up."
In the mod. Scand. tongues, except Icelandic and Færöese, the reduced form pa, paa, corresponding to Eng. (colloq. or dial.) 'pon, 'po', has displaced the simple prep. å, aa = on. [OED]