Apon feels like a misspelled Edition of "apron". If you are not referring to cooking use, It is really "on". act on/upon alight on/upon be conditioned on/on bread upon the waters by/on/upon request call upon probability upon occur upon make a decision on/on rely on/upon dilate on/on dote on/upon draw upon dwell on/upon embark on/on enlarge on/on d