musikalisch
musical
Having an aptitude or special talent for music.
Sie ist sehr musikalisch und spielt Klavier und Geige.
She is very musical and plays the piano and violin.

musical
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musical
Having an aptitude or special talent for music.
Sie ist sehr musikalisch und spielt Klavier und Geige.
She is very musical and plays the piano and violin.

The adjective 'musikalisch' (musical) is derived from the noun 'die Musik' (music). The ending '-alisch' indicates affiliation and is often used with words that come from other languages.
Die musikalische Begleitung war perfekt auf den Sänger abgestimmt.
The musical accompaniment was perfectly matched to the singer.
The exact meaning depends on the noun. If it refers to a person, it means 'talentiert' (talented). If it refers to a concept like 'Leitung' (direction/management), it means 'die Musik betreffend' (concerning music). If it refers to a voice, it means 'melodiös' (melodious).
Meine ganze Familie ist sehr musikalisch.
My whole family is very musical.
To express that someone has a talent for music, 'musikalisch' (musical) is often used predicatively with the verb 'sein' (to be). The structure is then: [person] ist musikalisch ([person] is musical).
Er ist nicht besonders musikalisch, aber er tanzt gern.
He is not especially musical, but he likes to dance.
When it means 'die Musik betreffend' (concerning music), 'musikalisch' (musical) often comes before abstract nouns. Common combinations are: 'die musikalische Leitung' (the musical direction), 'die musikalische Früherziehung' (early childhood music education), or 'ein musikalisches Werk' (a musical work).
In vielen Kindergärten wird musikalische Früherziehung angeboten.
Many kindergartens offer early childhood music education.
harmonious
'musikalisch' and 'harmonisch' can both describe something pleasant in the area of music. However, 'musikalisch' often says that someone has a talent for music or that something has to do with music. 'harmonisch' means more that notes fit together well or that something feels balanced. This can also apply to colors, shapes, or relationships. Learners may confuse the words because both sound positive. For a gifted person, you say 'musikalisch'. For good interplay, a calm impression, or a peaceful relationship, 'harmonisch' is more precise.

Meine Schwester ist sehr musikalisch und spielt seit Jahren Klavier.
My sister is very musical and has been playing the piano for years.
Die Stimmen im Chor klingen heute besonders harmonisch.
The voices in the choir sound especially harmonious today.