Etymology
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southwest (adv.)

Old English suð-west; see south + west. As a noun from early 12c. Related: Southwester; southwesterly. The nautical coat called a sou'wester (1836) protects the wearer against severe weather, such as a gale out of the southwest.

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south (adv.)

Old English suð "southward, to the south, southern, in the south," from Proto-Germanic *sunthaz, perhaps literally "sun-side" (source also of Old Saxon, Old Frisian suth "southward, in the south," Middle Dutch suut, Dutch zuid, German Süden), and related to base of *sunnon "sun" (from PIE root *sawel- "the sun"). Old French sur, sud (French sud), Spanish sur, sud are loan-words from Germanic, perhaps from Old Norse suðr.

As an adjective from c. 1300; as a noun, "one of the four cardinal points," also "southern region of a country," both late 13c. The Southern states of the U.S. have been collectively called The South since 1779 (in early use this often referred only to Georgia and South Carolina). South country in Britain means the part below the Tweed, in England the part below the Wash, and in Scotland the part below the Forth. South Sea meant "the Mediterranean" (late 14c.) and "the English Channel" (early 15c.) before it came to mean (in plural) "the South Pacific Ocean" (1520s) and it was frequent for "the Pacific Ocean" generally in U.S. in early 19c. (Thoreau, J.Q. Adams).

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by (prep., adv.)

Old English be- (unstressed) or bi (stressed) "near, in, by, during, about," from Proto-Germanic *bi "around, about," in compounds often merely intensive (source also of Old Saxon and Old Frisian bi "by, near," Middle Dutch bie, Dutch bij, German bei "by, at, near," Gothic bi "about"), from PIE *bhi, reduced form of root *ambhi- "around."

As an adverb by c. 1300, "near, close at hand."

OED (2nd ed. print) has 38 distinct definitions of it as a preposition. Originally an adverbial particle of place, which sense survives in place names (Whitby, Grimsby, etc., also compare rudesby). Elliptical use for "secondary course" was in Old English (opposed to main, as in byway, also compare by-blow "illegitimate child," 1590s, Middle English loteby "a concubine," from obsolete lote "to lurk, lie hidden"). This also is the sense of the second by in the phrase by the by (1610s).

By the way literally means "along the way" (c. 1200), hence "in passing by," used figuratively to introduce a tangential observation ("incidentally") by 1540s. To swear by something or someone is in Old English, perhaps originally "in the presence of." Phrase by and by (early 14c.) originally meant "one by one," with by apparently denoting succession; modern sense of "before long" is from 1520s.

By and large "in all its length and breadth" (1660s) originally was nautical, "sailing to the wind and off it," hence "in one direction then another;" from nautical expression large wind, one that crosses the ship's line in a favorable direction.

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drive-by (adj.)

as a modifier, "done from a moving vehicle," by 1989 (originally of shootings), from the verbal phrase; see drive (v.) + by (prep.).

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go south (v.)

"vanish, abscond," 1920s, American English, probably from mid-19c. notion of disappearing south to Mexico or Texas to escape pursuit or responsibility, reinforced by Native American belief (attested in colonial writing mid-18c.) that the soul journeys south after death.

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go-by (n.)

1640s, "an evasion, a leaving behind by artifice," from verbal phrase; see go (v.) + by (adv.). From 1650s as "a passing without notice, intentional disregard." Compare bygone.

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by-product (n.)

also byproduct, "secondary or additional product;" 1849, from by + product.

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South Africa 

1815 as a name for a distinct region that had been partly settled by Europeans; 1910 as the name of a nation.

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by-name (n.)

late 14c., "secondary name;" 1570s, "nickname," from by + name (n.).

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passer-by (n.)

also passerby, 1560s, from agent noun of pass (v.) + by; earlier, this sense was in passager (see passenger).

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