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

15th cent. From bello and -eza. Vulgar Latin *bellitsia?

Romance: Western Vulgar Latin: Portuguese beleza, Galician beleza, Catalan bellesa, Italian bellezza; Sardinian: bellesa
bello (Adjective) "beautiful"

13th cent. From Latin bellus 'id.' From Proto-Italic *dwen-elo- "good little thing." Derived from *dweno- "good" (see bueno).

Also the origin of the surnames Bel, Bella, and Bellas.

Romance: Western Vulgar Latin: Asturian bellu, Portuguese belo, Galician belo, Catalan bell, French beau, Italian bello, Istriot biel; Sardinian: bellu
berilo m. (Noun) "beryl"

17th cent. From Latin beryllus 'id.' Borrowed from Ancient Greek βήρυλλος ‎(béryllos) 'id.' Borrowed from a Dravidian language (compare Belur, a town in India).

Hellenic: Ancient Greek βηρύλλιον (beryllion)

Indo-Iranian: Indo-Aryan: Prakrit veḷuriya, veruliya; Sanskrit vaiḍūrya-
beso m. (Noun) "kiss"

13th cent. From Latin basium 'id.' Of unknown origin, probably a loan from a non-Indo-European language with a root *bu-/ba-.

Celtic: Goidelic: Middle Irish bus, pus "lip"

Germanic: West Germanic: English buss

Balto-Slavic: Baltic: Lithuanian bučiúoti

"The recent date of attestation renders a loanword likely. Since Catullus, who introduced the word into the written language, was from Verona, it might have been Celtic." ~ M. de Vaan, Etymological Dictionary of Latin (2014)
bien (Adverb, Adjective) "well"

Early 12th cent. From Latin bene 'id.,' from Old Latin *duened "good." From Proto-Italic *dweno- "good" (see bueno).

Romance: Western Vulgar Latin: Asturian bien, Portuguese bem, Galician ben, Catalan bé, ben, French bien, Italian bene; Eastern Vulgar Latin: Aromanian ghini, Romanian bine; Sardinian: beni.

The surprising sound shift from Old Latin du- to Latin b- is well documented: duonus "good" > bonus; duellum "war" > bellum.
bienvenido (Adjective) "welcome"

From bien and venir. A calque of Germanic words for "welcome" (i.e. well come).
bigote m. (Noun) "mustache"

Late 15th cent. First recorded as bigot de barva with -e later added via anaptyxis. Probably borrowed from Swiss German bî Gott "by God!," taken from Swiss German mercenaries during the Seige of Granada in 1483 - mercenaries who often sported prominent facial hair (Lapesa 1987). Previous theories hypothesized a borrowing from Old French bigot, slang for mustachioed Norman soldiers; from the Norman surname Bigot; or from Old French bigot "pastry resembling a mustache" (see Corominas 1991; Roberts 2015; Covarrubias 1611 respectively). Lapesa's theory has the benefit of both time and place for the word to enter into Spanish.

Also a metaphor for the remnant of drink on the upper lip (cf. English milk mustache).
blanca f. (Noun) "copper coin"

15th cent. Originally referring to silver coins minted during the reign King Juan II of Castile. The "white" referred to the silver content in the coin after whitening. A coin without the treatment was nicknamed negra or prieta. As silver content in the coin declined over time, the connection between "white" and the coin's luster weakened and came to refer to old copper or silver coins from the Medieval period. For a continuing etymology of blanca, see blanco.

For the origin of the surnames Blanca, Blancas, and Lablanca, the word was originally applied as a nickname to blond-headed women.
blanco (Adjective) "white"

12th cent. From Vulgar Latin *blancus 'id.' From a West Germanic source meaning "white" (compare Old High German blanc "shining," "white"). Ultimately from Proto-Germanic *blanka- "colorless."

For the origin of the surnames Blanco and Blancos, the word was originally applied as a nickname to blond-headed men.

Romance: Western Vulgar Latin: Asturian blancu, Portuguese branco, Galician branco, Catalan blanc, French blanc, Italian bianco

Germanic: North Germanic: Old Norse blakkr "black;" West Germanic: Old High German blanc

From the Western Romance dialect of Vulgar Latin.
blasfemar (Verb) "to blaspheme"

13th cent. A learned borrowing from Latin blasphemare 'id.' The native word is lastimar. Borrowed from Greek βλασφημεῖν (blasphemeîn) "to blaspheme," originally "to slander." Of unknown origin. The first element is mysterious; the second element is probably from φήμη (phéme) "reputation," "voice." From late Proto-Indo-European *bheh2-m̥h2- "reputation," also whence the word fama.