The story
- Proto-Indo-European · derived from*súHros
- Proto-Slavic · derived from*syřenьje“curdling”
- Bulgarian · borrowed fromсирене
- English todaysirene
From Bulgarian сирене (sirene), from Proto-Slavic *syřenьje (“curdling”), from Proto-Indo-European *súHros, whence also English sour, German sauer.
Words from the same roots
Proto-Indo-European*súHros all →
sour
Etymology from Wiktionary, CC BY-SA 4.0.