early 12c., from Old English uppan (prep.) "on, upon, up to, against," from up (adv.) + on (prep.); probably influenced by Scandinavian sources such as Old Norse upp a.
On, Upon. These words are in many uses identical in force, but upon is by origin (up + on) and in use more distinctly expressive of motion to the object from above or from the side. On has the same force, but is so widely used in other ways, and so often expresses mere rest, that it is felt by careful writers to be inadequate to the uses for which upon is preferred. [Century Dictionary, 1895]
late 14c., "acquire, get," from Old French encrochier "seize, fasten on, hang on (to), cling (to); hang up, suspend," literally "to catch with a hook," from en- "in" (see en- (1)) + croc "hook," from Old Norse krokr "hook" (see crook (n.)). Sense extended to "seize wrongfully" (c. 1400), then "trespass" (1530s). Related: Encroached; encroaches; encroaching.
1530s, "fasten or fix forcibly," from Latin impingere "drive into, strike against," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + pangere "to fix, fasten" (from PIE root *pag- "to fasten"). Sense of "encroach, infringe" first recorded 1738. Related: Impinged; impinging; impingent.
1520s, "impose a task upon;" 1590s, "to burden, put a strain upon," from task (n.). Related: Tasked; tasking.