Original meaning: 'kle' and 'zemer', two words in Yiddish & Hebrew, make up klezmer, meaning vessel of song = musical instrument.
A professional Jewish folk musician (the plural is 'klezmorim' or 'klezmers')
3. Music with its roots in Jewish eastern Europe. This is the most recent use of the word. Klezmer is pronounced with the 'z' as in 'zoo'.
From website: https://www.yiddishwit.com/gallery/klezmer.html
SOURCE: Stutchkoff, Der Oytser fun der Yidisher Shprakh. Literal translation: He's an expert like a goat's an expert on a musician. The Yiddish word klezmer refers to the musician, not the music.