1550s, "thrust forward forcibly or unduly" (trans.), from Latin obtrudere "to thrust into, press upon," from ob "in front of; toward" (see ob-) + trudere "to thrust," "to thrust, push," from PIE *treud- "to press, push, squeeze" (see threat). Intransitive sense of "be or become obtrusive, intrude, force oneself" is by 1570s. Related: Obtruded; obtruding.
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]
"an undue and unsolicited thrusting forward of something upon the notice or attention of others," 1570s, from Latin obtrusionem (nominative obtrusio), noun of action from past-participle stem of obtrudere "to thrust into, press upon" (see obtrude).
1520s, "impose a task upon;" 1590s, "to burden, put a strain upon," from task (n.). Related: Tasked; tasking.
1640s (transitive), "to brood upon, watch jealously" (figurative); 1721 in literal sense "to sit on (eggs) to hatch them," from Latin incubatus, past participle of incubare "to lie in or upon," also in the figurative sense "brood" (see incubation). Intransitive sense "to sit upon eggs" is from 1755. Related: Incubated; incubating.
