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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.
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.

Romance: Western Vulgar Latin: Portuguese música, Galician música, Catalan música, French musique, Italian musiche ; Eastern Vulgar Latin: 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.