Chopin wrote 27 of them

• Music practice pieces
• Some musical compositions
• Chopin's "Butterfly" et al.
• Musical practice pieces
• Musician's exercises
• Piano assignments
• Some works of Robert Schumann
• Piano school assignments

Wikipedia Word definitions in Wikipedia
Einojuhani Rautavaara's six Etydit (Études), Op. 42 were composed in 1969. According to the composer, the intent in writing these works, each of which explores a single interval , was to "...reintroduce a sonorous, broad piano style using the entire compass ...

Wiktionary Word definitions in Wiktionary
n. (plural of etude English)