Online Etymology Dictionary

bat (v.2): "to hit with a bat," mid-15c., from bat (n.1). Related: Batted; batting.
Bat Mitzvah: 1950, literally "daughter of command;" a Jewish girl who has reached age 12, the age of religious majority. Extended to the ceremony held on occasion of this.
Batavia: former name of Jakarta, capital of Indonesia, when it was the Dutch East Indies, a colony of the Netherlands; from Batavia, an ancient name for a region of Holland, from Latin Batavi, a people who dwelt between the Rhine and the Waal on the island of Betawe.
batch (n.): Old English *bæcce "something baked," from bacan "bake" (see bake (v.)). Batch is to bake as watch (n.) is to wake and match (n.2) "one of a pair" is to make. Extended 1713 to "any quantity produced at one operation."
bate (v.1): "to reduce, to lessen in intensity," c. 1300, shortening of abate (q.v.). Now only in phrase bated breath, which was used by Shakespeare in "The Merchant of Venice" (1596).
bate (v.2): c. 1300, "to contend with blows or arguments," from Old French batre "to hit, beat, strike," from Late Latin battere, from Latin batuere "to beat, knock" (see batter (v.)). In falconry, "to beat the wings impatiently and flutter away from the perch." Figurative sense of "to flutter downward" attested from 1580s.
bateau (n.): French-Canadian river boat, 1711, from French bateau, from Old French batel, from Germanic (see boat (n.)).
bated breath (n.): see bate (v.1).
batement (n.): mid-15c., shortening of abatement.
bath (n.): Old English bæð "immersing in water, mud, etc.," also "quantity of water, etc., for bathing," from Proto-Germanic *batham (source also of Old Norse bað, Middle Dutch bat, German bad), from PIE root *bhe- "to warm" (see fever) + Germanic *-thuz suffix indicating "act, process, condition" (as in birth, death). Original sense was of heating, not immersing in water. The city in Somerset, England (Old English Baðun) was so called from its hot springs. Bath salts attested from 1875 (Dr. Julius Braun, "On the Curative Effects of Baths and Waters").
bathe (v.): Old English baþian "to wash, lave, bathe" (transitive and intransitive), from root of bath (q.v.), with different vowel sound due to i-mutation. Related: Bathed; bathing.
bathetic (adj.): 1834, from bathos on the model of pathetic, which, however, does not come directly from pathos (see pathetic), so the formation is either erroneous or humorous. Bathotic (1863, perhaps on model of chaotic) is not much better.
bathing (n.): 1540s, verbal noun from bathe (v.). Bathing suit is recorded from 1852 (bathing costume from 1830); bathing beauty is 1920, from vaudeville.
batholith (n.): 1903, from German batholith (1892), coined by German geologist Eduard Suess (1831-1914) from Greek bathos "depth" (see benthos) + -lith "stone."
bathos (n.): "anticlimax, a descent from the sublime to the ridiculous," 1727, from Greek bathos "depth," related to bathys "deep" (see benthos). Introduced by Pope.
bathrobe (n.): also bath-robe, 1894, from bath (n.) + robe (n.).
bathroom (n.): 1780, from bath + room (n.). Originally a room with apparatus for bathing, used 20c. in U.S. as a euphemism for a lavatory and often noted as a word that confused British travelers. To go to the bathroom, euphemism for "relieve oneself; urinate, defecate," from 1920 (in a book for children), but typically used without regard for whether an actual bathroom is involved.
Bathsheba: Biblical wife of King David, mother of Solomon, from Hebrew Bathshebha, literally "daughter of the oath," from bath "daughter."
bathtub (n.): 1837, from bath + tub. Prohibition-era bathtub gin is recorded by 1928.
bathukolpian (adj.): "big-breasted," 1825, from Greek bathykolpos, literally "deep-bosomed," from bathys "deep" (see benthos) + kolpos "breast" (see gulf (n.)).
bathyscaphe (n.): "diving apparatus for reaching great depths," 1947, name coined by its inventor, Swiss "scientific extremist" Prof. Auguste Piccard (1884-1962), from Greek bathys "deep" (see benthos) + skaphe "light boat, skiff" (see skaphoid).
batik (n.): 1880, from Dutch, from Malay mbatik, said to be from amba "to write" + titik "dot, point."
batman (n.): "officer's servant," originally military title for "man in charge of a bat-horse and its load," 1755, from bat "pack-saddle" (late 14c.), from Old French bast (Modern French bât), from Late Latin bastum (see baton). Hence also batwoman (1941). The comic book hero dates from 1939.
baton (n.): 1540s, "a staff used as a weapon," from French bâton "stick, walking stick, staff, club, wand," from Old French baston (12c.) "stick, staff, rod," from Late Latin bastum "stout staff," probably of Gaulish origin or else from Greek *baston "support," from bastazein "to lift up, raise, carry." Meaning "staff carried as a symbol of office" is from 1580s; musical sense of "conductor's wand" is from 1841 (from 1839 as a French word in English). Often Englished 17c.-18c. as batoon.
Baton Rouge: city in Louisiana, U.S., a French translation of Choctaw itti homma "red pole," perhaps in reference to a painted boundary marker.
battalion (n.): 1580s, from Middle French bataillon (16c.), from Italian battaglione "battle squadron," from diminutive of Vulgar Latin battalia "battle," from Latin bauttere "to beat" (see batter (v.)). Specific sense of "part of a regiment" is from 1708.
Madame, lui répondit-il, ne vous y fiez pas: j'ay tôujours vû Dieu do coté des gros Batallions. [E.Boursault, 1702]
batten (n.): "strip of wood (especially used to fasten canvas over ships' hatches)," 1650s, Englished variant of baton "a stick, a staff" (see baton). Nautical use attested from 1769.
batten (v.1): "to improve; to fatten," 1590s, probably representing an English dialectal survival of Old Norse batna "improve" (source also of Old English batian, Old Frisian batia, Old High German bazen, Gothic gabatnan "to become better, avail, benefit," Old English bet "better;" also see boot (v.)). Related: Battened; battening.
batten (v.2): "to furnish with battens," 1775, from batten (n.); phrase batten down recorded from 1823. Related: Battened; battening.
Battenberg (n.): type of cake, 1903, from name of a town in Germany, the seat of a family which became known in Britain as Mountbatten.
batter (v.): "strike repeatedly, beat violently and rapidly," early 14c., from Old French batre "to beat, strike" (11c., Modern French battre "to beat, to strike"), from Latin battuere "to beat, strike," an old word in Latin, but almost certainly borrowed from Gaulish, from PIE root *bhau- "to strike" (source also of Welsh bathu "beat;" Old English beadu "battle," beatan "to beat," bytl "hammer, mallet"). Began to be widely used 1962 in reference to domestic abuse. Related: Battered; battering. Battering-ram is an ancient weapon (Latin aries), but the word attested only from 1610s.
batter (n.): "flour, eggs, and milk beaten together," late 14c., from Old French batteure "a beating," from Latin battuere "to beat, knock" (see batter (v.)).
battery (n.): 1530s, "action of battering," from Middle French batterie, from Old French baterie (12c.) "beating, thrashing, assault," from batre "beat," from Latin battuere "beat" (see batter (v.)).

Meaning shifted in Middle French from "bombardment" ("heavy blows" upon city walls or fortresses) to "unit of artillery" (a sense recorded in English from 1550s). Extension to "electrical cell" (1748, first used by Ben Franklin) is perhaps from the artillery sense via notion of "discharges" of electricity. In Middle English, bateri meant only "forged metal ware." In obsolete baseball jargon battery was the word for "pitcher and catcher" considered as a unit (1867, originally only the pitcher).
batting (n.): "sheets of cotton fiber," 1875, variant of obsolete bat "felted mass of fur, wool, etc.," from bat (n.1), on notion of "beaten" fabric.
battle (n.): c. 1300, from Old French bataille "battle, single combat," also "inner turmoil, harsh circumstances; army, body of soldiers," from Late Latin battualia "exercise of soldiers and gladiators in fighting and fencing," from Latin battuere "to beat, to strike" (see batter (v.)). Phrase battle royal "fight involving several combatants" is from 1670s.
battle (v.): early 14c., "to fight," from French batailler (12c.), from bataille (see battle (n.)). Related: Battled; battling.
battle-axe (n.): late 14c., weapon of war, from battle (n.) + axe (n.); meaning "formidable woman" is U.S. slang, first recorded 1896.
battledore (n.): mid-15c., "bat-like implement used in washing clothes," of unknown origin, perhaps from Old Provençal batedor, Spanish batidor "beater, bat," from batir "to beat;" perhaps blended with Middle English betel "hammer, mallet." As a trype of racket used in a game, from 1590s.
battlefield (n.): 1812, from battle (n.) + field (n.). The usual word for it in Old English was wælstow, literally "slaughter-place."
battlement (n.): early 14c., from Old French bataillement, earlier bastillement "fortification," from bastillier "to fortify, to equip with battlements," from bastille "fortress, tower" (see bastion). The raised parts are cops or merlons; the indentations are embrasures or crenelles.
battleship (n.): 1794, shortened from line-of-battle ship (1705), one large enough to take part in a main attack (formerly one of 74-plus guns); from battle (n.) + ship (n.). Later in U.S. Navy in reference to a class of ships that carried guns of the largest size. The last was decommissioned in 2006. Battleship-gray as a color is attested from 1916. Fighter and bomber airplanes in World War I newspaper articles were sometimes called battleplanes, but it did not catch on.
battology (n.): "needless repetition in speaking or writing," c. 1600, from Greek battologia "a speaking stammeringly," from battos "stammerer," of imitative origin, + -logia (see -logy).
batty (adj.): 1580s, "pertaining to bats," from bat (n.2) + -y (2). Slang sense "nuts, crazy" is attested from 1903, from the expression (to have) bats in (one's) belfry, also meaning "not be right in the head" (1899).
bauble (n.): "showy trinket or ornament," early 14c., from Old French baubel "child's toy, trinket," probably a reduplication of bel, from Latin bellus "pretty" (see bene-). Or else related to babe, baby.
baud (n.): 1932, originally a unit of speed in telegraphy, coined in French in 1929 in honor of French inventor and engineer Jean-Maurice-Émile Baudot (1845-1903), who designed a telegraph printing system.
Bauhaus (n.): 1923, from German Bauhaus, literally "architecture-house;" school of design founded in Weimar, Germany, 1919 by Walter Gropius (1883-1969), later extended to the principles it embodied. First element is bau "building, construction, structure," from Old High German buan "to dwell" (see bound (adj.2)). For second element, see house (n.).
baulk: alternative spelling of balk, especially in billiards, in reference to a bad shot.
bauxite (n.): 1861, clayey mineral containing aluminum, from French bauxite (1821), from Les Baux, near Soles, where it was first found. The place name is from Provençal Li Baus, literally "the precipices."
Bavaria: named for the Boii, ancient Celtic people who once lived there (also see Bohemia).
bawd (n.): a complicated word of uncertain history. First attested late 15c., "lewd person" (of either sex; since c. 1700 applied only to women), probably from baude-strote "procurer of prostitutes" (mid-14c.), which may be from Middle English bawde (adj.) "merry, joyous," from Old French baud "gay, licentious" (from Frankish *bald "bold" or some such Germanic source). It would not be the first time a word meaning "joyous" had taken on a sexual sense. The sense evolution shading from "bold" to "lewd" is not difficult; compare Old French baudise "ardor, joy, elation, act of boldness, presumption;" baudie "elation, high spirits," fole baudie "bawdry, shamelessness." The Old French word also is the source of French baudet "donkey," in Picardy dialect "loose woman."

The second element in baude-strote would be trot "one who runs errands," or Germanic *strutt (see strut). But OED doubts all this. There was an Old French baudestrote, baudetrot of the same meaning (13c.), and this may be the direct source of Middle English baude-strote. The obsolete word bronstrops "procuress," frequently found in Middleton's comedies, probably is an alteration of baude-strote.