The only free and comprehensive online etymological dictionary of the Spanish language
grupo m. (Noun) "group"
15th cent. meaning "group of clouds." The modern sense is first recorded in the 18th cent. Borrowed from Italian gruppo 'id.,' itself borrowed from Old Occitan grupo, which in turn was borrowed from a Germanic source. Ultimately from Proto-Germanic *kruppa- "body (of things)." Derived from Proto-Indo-European *gru̯bh-néh2- "to crawl" from a sense of crumpling up.
Indo-European
Germanic
Old Norse kroppr "body," Old High German kropf "goiter," Old English crop "sprout" (English crop)
guacamole m. (Noun) "avocado-based salad," "avocado condiment"
Very late 19th cent. From Nahuatl ahuacaoulli 'id.,' comprised of ahuacatl "avocado" and molli "sauce." See aguacate and mole (3) respectively.
guardia f. (Noun) "guard"
12th cent. Borrowed from Gothic *wardja "watchman." Derived from the verb in Proto-Germanic *warjan- "to prevent." From Proto-Indo-European *h2u̯or-éi̯e- 'id.'
Also the origin of the surnames Guardia, Guarda, La Guardia, Laguardia, and Guardias.
Indo-European
Germanic
Gothic warjan, Old Norse verja, Old Saxon werian, Old High German werren, Old English werian
Balto-Slavic
Lithuanian vérti "to pierce," Latvian vẽrt "to open"
Hellenic
Ancient Greek ἀείρειν (aeírein) "to raise"
Indo-Iranian
Sanskrit vr̥ṇóti "to cover," Young Avestan vərənaoti 'id.'
guay (Interjection) "woe!;" (Spain) "great!"
13th cent. There are three origin theories of this word. If a majority of linguists is to be taken as some sort of consensus, then guay is probably from Latin "woe." Alternatively, the word is from Gothic wai "woe." From Proto-Germanic *wai 'id.' Both Latin and Proto-Germanic *wai trace back to Proto-Indo-European *u̯ai̯ 'id.' A third idea is that the word is from Andalusian Arabic *way. See Dworkin (2012) for further discussion.
Variants
Old Spanish guayar "to wail," guaya "wailing"
Indo-European
Romance
Italian guai, Romanian çai
Celtic
Old Irish fáe "alas," Middle Welsh gwae 'id.,' Middle Breton goa'id.'
Germanic
Old Norse vei "woe," Old High German "woe," Old Saxon 'id.,' Old English (English woe)
Balto-Slavic
Latvian vai
Armenian
Armenian vay
Indo-Iranian
Avestan vaii-ōi (?)
The Spanish sense of "great" is a secondary formation through meaning reversal.
guerra f. (Noun) "war"
11th cent. Disputed etymology. Certainly from a Germanic source. Following Corominas (1991) and Roberts (2014), perhaps Proto-West Germanic *werra "confusion (of battle)," or a similar meaning. From there, the traditional etymology is from Osthoff (1910) that posits an origin in Proto-Germanic *wersa- "confusion," "disruption," "greater evil." From Proto-Indo-European *u̯ers- "to confuse."
Also the origin of the surnames Guerra and Guerro.
gustar (Verb) "to please," "to like;" "to taste"
13th cent. Old Spanish gostar. From Latin gustare "to taste." From gustus "tasting" (see gusto).
Indo-European
Romance
Portuguese gostar, Catalan gustar, French goûter, Italian gustare, Aromanian gustu, Romanian gusta, Sardinian gustare
Over time, the meaning drifted from "to taste" to "pleasing (in taste)" to "pleasing."
gusto (Noun) "taste;" "pleasure"
Very early 15th cent. Old Spanish gosto. From Latin gustus 'id.' From Proto-Italic *gustu- 'id.' From Proto-Indo-European *ǵu̯s-tu̯- 'id.' From ǵeu̯s- "to taste."
Indo-European
Romance
Portuguese gosto, Catalan gust, French goût, Italian gusto, Aromanian gustu, Romanian gust, Sardinian gustu
gym m. (Noun) "gymnasium"
Borrowed from English gym, apocopation from earlier gymansium, itself from Latin gymansium 'id.' (see gimnasio.