The only free and comprehensive online etymological dictionary of the Spanish language
muerto (2) (Noun) "dead person"
10th cent. From Latin mortuus 'id.' Old Latin mortuos. From Proto-Italic *mortwo- 'id.' From Proto-Indo-European *mr̥-t-u̯o 'id.,' but the original form was likely *mr̥-to- 'id.
Indo-European
Italic
Venetic murtuvoi "to the dead"
mujer f. (Noun) "woman"
11th cent. Old Spanish muller. 12th cent. Old Spanish mugier, muger. From Latin mulier 'id.' Possibly a comparative of mollis "soft," "weak" but see de Vaan (2014) for a discussion of this argument's serious problems. If not connected to mollis, then of unknown origin. For a continued etymology of mollis, see muelle.
Indo-European
Romance
Asturian muyer, Portuguese mulher, Galician muller, Catalan muller, Italian moglie, Aromanian muljari, Romanian muiere, Sardinian mugere
mundo m. (Noun) "world"
12th cent. From Latin mundus 'id.' Ultimately of unknown origin. According to de Vaan (2014), a connection to Etruscan munθ- "cannot be established as long as its meaning is unknown."
Indo-European
Romance
Asturian mundu, Portuguese mundo, Galician mundo, Catalan món, French monde, Italian mondo, Sardinian mundhu
Tyrsenian
munθ-?, meaning unknown
On the basis of Auto de Reyes Magos (12th cent.), it is believed that mundo was pronounced /mon.do/ for some time: Que es senior de todo el mundo / asi cumo el cilo es redondo. This conservative pronunciation was likely due to reinforcement from Ecclesiastical Latin and, perhaps, from Gallo-Romance languages like French, Catalan, which meant that for several centuries there were two pronunciations of mundo side-by-side.
muñir (Verb) "to summon"
From Latin monere "to remind." From Proto-Italic *mon-eje- 'id.' From Proto-Indo-European *mon-ei̯e- 'id.' More literally to cause upon another's mind (cf. mente "mind"), from *men- "to think" (see mente).
Indo-European
Romance
Portuguese monir
Celtic
Celtiberian monimam (?) "memory," Old Irish muinithir "to think"
Indo-Iranian
Sanskrit mānáyati "to honor," Old Avestan mānaiia- "to make think"
muñir (Verb) to summon
From Latin monere "to warn," "to remind." From Proto-Italic *mon-eje- "to warn," "to remind." From Proto-Indo-European *mon-ei̯e- 'id.'
Indo-European
Romance
Portuguese monir
Celtic
Old Irish muinethar "to think"
Hellenic
Ancient Greek μαίνομαι (maínomai) "I am angry"
Indo-Iranian
Sanskrit mānyáti "he honors," Old Avestan mānaiia- "to make think"
mur m. (Noun) (archaic) "mouse"
13th cent. From Latin murem, accusative of mus 'id.' From Proto-Italic *mūs 'id.' From Proto-Indo-European *muHs 'id.'
Indo-European
Romance
Asturian mure, Portuguese muro
Germanic
Old Norse mús "mouse," "biceps," Old High German mūs Old Saxon mūs 'id.,' Old English mūs 'id.' (English mouse)
Albanian
Albanian "mouse"
Balto-Slavic
Old Church Slavonic myšь "mouse," Russian myš' 'id.,' Czech myš 'id.,' Slovene mìš 'id.'
Hellenic
Ancient Greek μῦς (mûs) "mouse"
Armenian
Armenian mikn "mouse"
Indo-Iranian
Sanskrit mū́ṣ- "mouse," "rat," Young Avestan mūš-, name of a Pairika
Tocharian
B maścītse "mouse," "rat"
murcielago, murceguillo m. (Noun) "bat"
Both variants are from 13th cent. murciégalo, itself from murciego. See mur and ciego respectively.
musa f. (Noun) "Muse;" "inspiration"
15th cent. borrowing from Latin Musa 'id.,' from Ancient Greek Μοῦσα ‎(Moûsa). Its origins are hazy. Possibly from Proto-Indo-European *mondh-i̯h2 "the wise one" as an appellation for a Muse. In which case, the name stretches back to an original root *men- "to think" (see mente). But Beekes (2014) notes, the word with its difficult origin may just as well be a loan from a Pre-Greek source.
"The Muses can assist by putting the poet in mind of the relevant material. This is why they are called daughters of Memory, Mnemosyne." M. West, Indo-European Poetry and Myth (2007)
música f. (Noun) "music"
13th cent. From Latin musica 'id.,' borrowed from Ancient Greek μουσική ‎(mousiké) "art," originally the art of the Muses. Part of a longer phrase μουσική ‎τέχνη (mousiké tékhne) "Muse's art." For a continued etymology of μουσική ‎(mousiké) and the name Muse, see musa.
Indo-European
Romance
Portuguese música, Galician música, Catalan música, French musique, Italian musiche, Romanian muzică
muy (Adverb) "very"
10th cent. Old Spanish muit. Apocapation of muito (see mucho). It was used in variation with much(o) until the 15th cent.