The only free and comprehensive online etymological dictionary of the Spanish language
botella f. (Noun) "bottle"

18th cent. Borrowed from French bouteille 'id.' From Latin butticula "little wineskin." From buttis "wineskin" (see bote (3)).
brazo m. (Noun) "arm"

11th cent. From Latin bracchium 'id.' Borrowed from Ancient Greek βραχίων ‎(brakhíon) 'id.' Of unknown origin.

Also responsible for the surnames Brazo and Brazos, given to men in respect of their physical strength.

Romance: Western Vulgar Latin: Asturian brazu, Portuguese braço, Galician brazo, Catalan braç, French bras, Italian braccio, Dalmatian braz; Eastern Vulgar Latin: Aromanian brats, Romanian braț; Sardinian: baltzu
brillante (Adjective) "brilliant"

17th cent. From brillar.

Romance: Western Vulgar Latin: Asturian (Palluezu) brillante, Portuguese brilhante, Galician brillante, Catalan brillant, French brillant, Italian brillante
brillar (Verb) "to shine"

17th cent. Borrowed from Italian brillare 'id.' From Vulgar Latin *beryllare "to shine (like a beryl gemstone)." From Latin beryllus "beryl" (see berilo).
broma (1) f. (Noun) "joke," "jest"

Very early 16th cent. Originally meaning "shipworm" (compare Asturian broma / groma which can mean both "jest" or "shipworm"). It came to mean something serious and destructive; later something bothersome; and finally a jest. Borrowed from Ancient Greek βρῶμα ‎(brôma) "shipworm." From Proto-Indo-European *gwerh3- "to devour."

Romance: Western Vulgar Latin: Asturian broma "joke," "shipworm," Galician broma, Catalan broma "joke," "fog,"

Indo-European: Balto-Slavic: Old Church Slavonic žьrǫ, Lithuanian gìrtas "drunk;" Armenian: eker "he devoured" (h1e-gwerh3-et); Indo-Iranian: Sanskrit gīrṇá- "devoured"
broma (2) f. (Noun) "dough;" "oat porridge"

19th cent. A feminine form created by folk etymology from Latin bromos "oats." Borrowed from Ancient Greek βρόμος (brómos) 'id.' Of unknown origin. Probably from a non-Indo-European language.

Hellenic: Ancient Greek βόρμος (bórmos) "oats"
bueno (Adjective, Interjection) "good;" "well"

11th cent. From Latin bonus, from Old Latin duenos. From Proto-Italic *dwenos 'id.' Of difficult etymology, despite cognates in other Indo-European languages. There is no convincing reconstruction in Proto-Indo-European that would yield *dwe- in Proto-Italic. De Vaan (2014) tentatively hypothesizes *du̯h2-eno-, but this would become *dwano- in Proto-Italic. If the original root in Proto-Indo-European was *dh3u̯o- (from *deh3- "to give;" see dar) then a suffix *-eno- is merely an ad hoc explanation, for aside from this solitary word there is no evidence for the existence of a putative *-eno- (Mayrhofer 1992).

As a surname, it was originally given to those said to be of good omen.

Romance: Western Vulgar Latin: Asturian bonu, Portuguese bom, Galician bo, Catalan bo, French bon, Italian buono; Eastern Vulgar Latin: Aromanian bun, Romanian bun; Sardinian: bonu

Italic: Faliscan duenas "of the brave," duenom "brave"

The surprising sound shift from Old Latin du- to Latin b- is well documented: duonus "good" > bonus; duellum "war" > bellum.
-bula, -bla- Instrumental suffix.

Fossilized in Spanish. From Latin -bula 'id.' From Proto-Italic *-þlo- 'id.' From Proto-Indo-European *-dhlo- 'id.'

Romance: Western Vulgar Latin *-bla-: Asturian -la-, Portuguese -la-, Galician -la-, Catalan -ula- (*-bula-), French -bl(e)-, Italian -ba-; Eastern Vulgar Latin: Romanian -bulă (learned borrowing); Extra-Comparanda: English -ble (borrowed from Old French -ble

Indo-European: Balto-Slavic *-mi: Lithuanian -mi, Old Church Slavonic -mĭ; Armenian *-bhi: -b; Hellenic *-bhi: Mycenaean -pi; Indo-Iranian: Sanskrit (inst. pl.) -dhís

Present in words like fábula, but less obviously in words like the -bl- in hablar.
bus m. (Noun) "bus"

Borrowed from French bus 'id.,' a clipping of earlier omnibus "for all." The name omnibus was applied by Jacques Lafitt in 1820 as part of a larger phrase that did not survive: voiture omnibus "coach for all" (Walsh 1913).
buscar (Verb) "to search for"

12th cent. Unknown origin but present in some form in Western Vulgar Latin. Perhaps from a hypothetical Vulgar Latin verb *boscare, derived from *boscus "woods," in the sense of searching for kindling. See bosque.

Romance: Western Vulgar Latin: Asturian buscar "to search," (Palacios del Sil) "to find," Aragonese buscar, Leonese buscare, Portuguese buscar, Galician busca, Italian buscare "to acquire."