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down (adv.)[down 词源字典]: late Old English shortened form of Old English ofdune "downwards," from dune "from the hill," dative of dun "hill" (see down (n.2)). A sense development peculiar to English.

Used as a preposition since c. 1500. Sense of "depressed mentally" is attested from c. 1600. Slang sense of "aware, wide awake" is attested from 1812. Computer crash sense is from 1965. As a preposition from late 14c.; as an adjective from 1560s. Down-and-out is from 1889, American English, from situation of a beaten prizefighter. Down home (adj.) is 1931, American English; down the hatch as a toast is from 1931; down to the wire is 1901, from horse-racing. Down time is from 1952. Down under "Australia and New Zealand" attested from 1886; Down East "Maine" is from 1825; Down South "in the Southern states of the U.S." is attested by 1834.[down etymology, down origin, 英语词源]
fly (adj.): slang, "clever, alert, wide awake," by 1811, perhaps from fly (n.) on the notion of the insect being hard to catch. Other theories, however, trace it to fledge or flash. Slang use in 1990s might be a revival or a reinvention.
wide (adj.): Old English wid "vast, broad, long," also used of time, from Proto-Germanic *widaz (cognates: Old Saxon, Old Frisian wid, Old Norse viðr, Dutch wijd, Old High German wit, German weit), perhaps from PIE *wi-ito-, from root *wi- "apart, away, in half."

Meaning "distended, expanded, spread apart" is from c. 1500; sense of "embracing many subjects" is from 1530s; meaning "missing the intended target" is from 1580s. As a second element in compounds (such as nationwide, worldwide) meaning "extending through the whole of," is is from late Old English. As an adverb, Old English wide. Wide open "unguarded, exposed to attack" (1915) originally was in boxing, etc. Wide awake (adj.) is first recorded 1818; figurative sense of "alert, knowing" is attested from 1833.