The only free and comprehensive online etymological dictionary of the Spanish language
banda (1) f. (Noun) "bandage strip," "tape"
12th cent. Borrowed from Old French bande 'id.' Borrowed from a Germanic source, perhaps Proto-West-Germanic *banda- "band," "bond." From Proto-Germanic *banda- 'id.' From Proto-Indo-European *bhondh-o- 'id.' From the root *bhendh- "to bind."
Indo-European
Germanic
Old Norse band, Old Saxon band, Old English beand (English band)
Indo-Iranian
Young Avestan baṇda- "bond"
banda (2) f. (Noun) "band," "group"
16th cent. Borrowed from Old French bande 'id.,' itself borrowed from Old Occitan banda "regiment." Prior to the modern military sense, banda had been borrowed from Old French bande "group" in the 14th cent. to mean "flock," but was replaced by the later meaning. Borrowed from Gothic *bandwa "sign." A *bandwa referred to the banner or flag carried by a regiment, and was later applied to the regiment itself. From Proto-Germanic *bandwa- 'id.' Frorm Proto-Indo-European *bhonh2-tu̯éh2- 'id.' From the verb *bhó-n-h2-e- "to summon." From the root *bheh2- "to say" (see hablar).
Indo-European
Germanic
Gothic bandwo, Old Norse benda "to signal"
baño m. (Noun) "bath"
11th cent. From Vulgar Latin baneum 'id.,' from Latin balneum - a syncopated variant of the more conservative balineum - borrowed from Greek βαλανεῖον (balaneîon) "bath," "bathing room." A Pre-Greek substrate word.
Found as the name of the village of Baño in Galicia. In the feminine, found in the village name La Baña, used throughout Leon and Galicia. In the plural it is a common toponym throughout Spain, dating back to the public bath houses of Roman times. Also the origin of the Valencian surname Buñol and the Navarran surname Buñuel.
Indo-European
Romance
Asturian bañu, Portuguese banho, Galician baño, Catalan bany, French bain, Italian bagno, Romanian baie
"For a term for bathing in warm water, which is probably an Aegaean custom, we might expect a Pre-Greek origin." ~ Robert S. P. Beekes (2014).
bar m. (Noun) "bar," "tavern"
Borrowed from English bar, originally referring to a bar's countertop, itself borrowed from Old French bar "support." From Vulgar Latin *barra 'id.' The native word in Spanish is barra.
barca f. (Noun) "small ship"
12th cent. From Late Latin barca 'id.,' from Vulgar Latin *barica 'id.' From Latin baris "boat" with diminutive suffix -ica added. The word was borrowed from Greek βάρις (báris) "boat," (originally referring to Egyptian boats). A loanword from Coptic baare "small boat."
Also the origin of the surnames Barca and Barcas.
Indo-European
Romance
Asturian barca, Portuguese barca, Galician barca, Catalan barca, French barque, Italian barca, Romanian barcă
barco m. (Noun) "ship"
13th cent. From barca.
Also the origin of the surnames Barco, del Barco, Delbarco and Barcos.
Indo-European
Romance
Asturian barcu, Portuguese barco
barra f. (Noun) "bar"
13th cent. From Vulgar Latin *barra 'id.' Of unknown origin.
The word is the origin behind Barra, the name of villages in Galicia and Asturias. Also the origin of the surname de la Barra.
Indo-European
Romance
Asturian barra, Portuguese barra, Galician barra, Catalan barra, French barre, Italian barra, Romanian bară
Basque
Basque marra "line" (borrowed from Vulgar Latin)
barrer (Verb) "to sweep"
13th cent. From Latin verrere 'id.' (Old Latin vorrere). From Proto-Italic *wors-e/o- 'id.' From Proto-Indo-European *u̯rs-e/o- "to wipe," "to harvest."
Indo-European
Romance
Asturian barrer, Portuguese varrer, Galician varrer
Balto-Slavic
Russian Church Slavic vьrxu "to thresh"
Barri m. (Toponym) meaning unknown (possibly "countryside," "forest," "corral")
Of uncertain origin. Tibón (1988) says to be from an old Basque word barri, meaning "'campo', 'plantel", 'bosque', 'corral'." (See also Barrio (2).) However, Tibón's entry is woefully under-argued. How does he reach his putative definition of the word? Was it by merely describing the geography of the places? What other evidence is there for this word? To wit, the only possible cognate is aberri "fatherland" (from aba "father" and herri "country"); yet this word was minted in the 1890s, very recent to be the source.

Perhaps more convincingly, however, is that the name comes from Basque barri "new," from Proto-Basque *berr- 'id.' Unfortunately this etymology is plagued by questions of its own: How, why, and when did the adjective become an adjectival?
barrio (1) m. (Noun) "neighborhood"
10th cent. Borrowed from Andalusian Arabic barri "outskirts."
Not the origin of the surname Barrio.