On; used in all the senses of that word, with which it is interchangeable. Upon an hill of flowers. Our host upon his stirrups stood anon. (Chaucer) Thou shalt take of the blood that is upon the altar. (Ex. Xxix. 21) The philistines be upon thee, samson. (Judg. Xvi. 9) As I did stand my watch upon the hill. (Shak) He made a great difference between people that did rebel upon wantonness, and them that did rebel upon want. (bacon) This advantage we lost upon the invention of firearms. (Addison) Upon the whole, it will be necessary to avoid that perpetual repetition of the same epithets which we find in homer. (pope) He had abandoned the frontiers, retiring upon Glasgow. (Sir. W. Scott) Philip swore upon the Evangelists to abstain from aggression in my absence. (Landor)
Upon conveys a more distinct notion that on carries with it of something that literally or metaphorically bears or supports. It is less employed than it used to be, on having for the most part taken its place. Some expressions formed with it belong only to old style; as, upon pity they were taken away; that is, in consequence of pity: upon the rate of thirty thousand; that is, amounting to the rate: to die upon the hand; that is, by means of the hand: he had a garment upon; that is, upon himself: the time is coming fast upon; that is, upon the present time. By the omission of its object, upon acquires an adverbial sense, as in the last two examples. To assure upon, to promise; to undertake. To come upon. See Come. To take upon, to assume.
Origin: AS. Uppan, uppon; upp 424 up _ on, an, on. See Up, and On.