buy (n.) Look up buy at Dictionary.com
"a purchase," especially a worthwhile one, 1875, American English, from buy (v.).
buy-in (n.) Look up buy-in at Dictionary.com
"act of obtaining an interest in," 1970, from verbal phrase buy in "to purchase a commission or stock" (1826), from buy (v.) + in (adv.). To buy into "obtain an interest in by purchase" (as of stock shares) is recorded from 1680s.
buy-out (n.) Look up buy-out at Dictionary.com
also buy-out, "the purchasing of a controlling share in a company," 1961, from verbal phrase buy out "purchase (someone's) estate and turn him out of it," 1640s, from buy (v.) + out (adv.).
buyer (n.) Look up buyer at Dictionary.com
c. 1200, biggere "one who purchases," agent noun from buy (v.). Meaning "one whose job is to buy goods for a store" is from 1884. Buyer's market attested from 1886.
buzkashi (n.) Look up buzkashi at Dictionary.com
Afghan sport, a sort of mounted polo played with a goat carcass, 1956, from Persian buz "goat" + kashi "dragging, drawing."
buzz (n.) Look up buzz at Dictionary.com
"a busy rumour" [Rowe], 1620s (earlier "a fancy," c. 1600), figurative use from buzz (v.). Literal sense of "a humming sound" is from 1640s. A "buzz" was the characteristic sound of an airplane in early 20c.; hence verbal sense "to fly swiftly," by 1928; by 1940 especially in military use, "to fly low over a surface as a warning signal" (for example that target practice is about to begin):
The patrol aircraft shall employ the method of warning known as "buzzing" which consists of low flight by the airplane and repeated opening and closing of the throttle. [1941 Supplement to the Code of Federal Regulations of the United States of America," Chap. II, Corps of Engineers, War Department, p. 3434, etc. ]
Meaning "pleasant sense of intoxication" first recorded 1935. The children's game of counting off with 7 or multiples of it replaced by buzz is attested from 1864 and is mentioned in "Little Women" (1868). To give (someone) a buzz (by 1922) is from the buzz that announced a call on old telephone systems (1913). Buzz bomb "V1 rocket" is from 1944.
buzz (v.) Look up buzz at Dictionary.com
late 15c. (buzzing is from late 14c.), echoic of bees and other insects. Aviation sense of "fly low and close" is by 1941 (see buzz (n.)). Related: Buzzed. To buzz off "go away quickly" (1914) originally meant "to ring off on the telephone," from the use of buzzers to signal a call or message on old systems. As a command, it originally would have been telling someone to get off the line.
buzz-cut (n.) Look up buzz-cut at Dictionary.com
by 1973, American English, from buzz (n.), perhaps from the sound of the barber's electric clipper, + cut (n.) in the "haircut" sense.
buzz-saw (n.) Look up buzz-saw at Dictionary.com
"circular saw," 1849, American English, from buzz (v.) + saw (n.). So called from the sound it makes when in operation.
buzzard (n.) Look up buzzard at Dictionary.com
c. 1300, "type of hawk not used in falconry," from Old French buisart "harrier, inferior hawk," from buson, buison, apparently from Latin buteonem (nominative buteo) a kind of hawk ("but the process of formation is not evident" - OED), perhaps with -art suffix for one that carries on some action or possesses some quality, with derogatory connotation (see -ard). In the New World extended to the American vulture (by 1830s). De Vaan says buteo is "Probably onomatopoeic, rendering the call of a hawk or buzzard."
buzzer (n.) Look up buzzer at Dictionary.com
c. 1600, "buzzing insect," agent noun from buzz (v.). Used 1870s in Britain of steam-powered whistles used to call or dismiss factory workers. In reference to electricity-powered mechanical devices that buzz, from 1882.
buzzword (n.) Look up buzzword at Dictionary.com
also buzz word, 1946, from buzz (n.) + word (n.). Noted as Harvard student slang for the key words in a lecture or reading. Perhaps from the use of buzz in the popular counting game.
BVDs (n.) Look up BVDs at Dictionary.com
"men's underwear," 1935, from trademark name (dating to 1876) of manufacturer Bradley, Voorhees, and Day.
bwana Look up bwana at Dictionary.com
respectful or reverential form of address in East Africa, 1875, from Swahili.
by (prep., adv.) Look up by at Dictionary.com
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.
by-name (n.) Look up by-name at Dictionary.com
late 14c., "secondary name;" 1570s, "nickname," from by + name (n.).
by-path (n.) Look up by-path at Dictionary.com
"side road," late 14c., from by + path.
by-product (n.) Look up by-product at Dictionary.com
also byproduct, "secondary or additional product;" 1849, from by + product.
by-road (n.) Look up by-road at Dictionary.com
"side road," 1670s, from by + road.
Byblos Look up Byblos at Dictionary.com
ancient Phoenician port (modern Jebeil, Lebanon) from which Egyptian papyrus was exported to Greece. The name probably is a Greek corruption of Phoenician Gebhal, said to mean literally "frontier town" or "mountain town" (compare Hebrew gebhul "frontier, boundary," Arabic jabal, Canaanite gubla "mountain"), which is perhaps a folk-etymology of the older Phoenician name, which might contain El "god." The Greek name also might have been influenced by, or come from, an Egyptian word for "papyrus."
bye (interj.) Look up bye at Dictionary.com
1709, shortened form of good-bye. Also compare lullaby. Reduplication bye-bye is recorded from 1736; as a sound used to lull a child to sleep it is attested from c. 1500.
bye (n.) Look up bye at Dictionary.com
in sporting use, a variant of by (prep). Originally in cricket, "a run scored on a ball that is missed by the wicket-keeper" (1746); later, in other sports, "position of one who is left without a competitor when the rest have drawn pairs" (1868).
bygone (adj.) Look up bygone at Dictionary.com
"that has gone by, past," early 15c., from by (adv.) + gone. Compare similar construction of aforesaid. As a noun from 1560s (see bygones).
bygones (n.) Look up bygones at Dictionary.com
"things that are past, what has gone by," especially offenses, 1560s, from plural of noun use of bygone (q.v.).
bylaw (n.) Look up bylaw at Dictionary.com
also by-law, late 13c., bilage "local ordinance," from Old Norse or Old Danish bi-lagu "town law," from byr "place where people dwell, town, village," from bua "to dwell" (from PIE root *bheue- "to be, exist, grow") + lagu "law" (see law). So, a local law pertaining to local residents, hence "a standing rule of a corporation or association for regulation of its organization and conduct." Sense influenced by by.
byline (n.) Look up byline at Dictionary.com
also by-line, 1926, "line giving the name of the writer of an article in a newspaper or magazine;" it typically reads BY ________. From by (prep.) + line (n.). As a verb by 1942. Related: Bylined.
BYOB Look up BYOB at Dictionary.com
initialism (acronym) for "bring your own bottle" or "bring your own booze," by 1951.
bypass (n.) Look up bypass at Dictionary.com
also by-pass, 1848, "small pipe passing around a valve in a gasworks" (for a pilot light, etc.), from the verbal phrase; see by + pass (v.). First used 1922 for "road for the relief of congestion;" figurative sense is from 1928. The heart operation was first so called 1957.
bypass (v.) Look up bypass at Dictionary.com
1823, "to pass by" (implied in bypassed), from the verbal phrase; see by + pass (v.). From 1928 as "to go round, avoid;" figurative use from 1941. Related: Bypassed; bypassing.
byre (n.) Look up byre at Dictionary.com
"cow-shed, shelter for cattle," Old English byre, perhaps related to bur "cottage, dwelling, house" (see bower).
Byronic (adj.) Look up Byronic at Dictionary.com
1823, pertaining to, characteristic of, or resembling British poet George Gordon, 6th Baron Byron (1788-1824) or his poetry.
Perfect she was, but as perfection is
Insipid in this naughty world of ours,
Where our first parents never learn'd to kiss
Till they were exiled from their earlier bowers,
Where all was peace, and innocence, and bliss
(I wonder how they got through the twelve hours),
Don Jose like a lineal son of Eve,
Went plucking various fruit without her leave.

[from "Don Juan"]
bystander (n.) Look up bystander at Dictionary.com
"spectator, one who stands near," 1610s, from by + agent noun from stand (v.). They have been innocent at least since 1829. Stander-by is from 1540s.
byte (n.) Look up byte at Dictionary.com
"unit of digital information in a computer," typically consisting of eight bits, 1956, American English; see bit (n.2). Reputedly coined by German-born American computer scientist Werner Buchholz (b. 1922) at IBM.
byway (n.) Look up byway at Dictionary.com
"a private, secluded, or out-of-the-way path or road," mid-14c., from by + way (n.).
byword (n.) Look up byword at Dictionary.com
also by-word, late Old English biword "proverb, word or phrase used proverbially;" see by + word (n.). Formed on the model of Latin proverbium or Greek parabole. Meaning "something that has become proverbial" (usually in a satirical or bad sense) is from 1530s.
Byzantine (adj.) Look up Byzantine at Dictionary.com
pertaining to Byzantium (q.v., original name of Constantinople, modern Istanbul), 1770, from Late Latin Byzantinus; originally used of the style of art and architecture developed there 4c.-5c. C.E.; later in reference to the complex, devious, and intriguing character of the royal court of Constantinople (1937). As a noun from 1770. Byzantian is from 1610s.
Byzantium Look up Byzantium at Dictionary.com
ancient Greek settlement in Thrace on the European side of the Bosphorus, said to be named for its 7c. B.C.E. founder, Byzas of Megara. A place of little consequence until 330 C.E., when Constantine the Great re-founded it and made it his capital (see Constantinople).