From Proto-Italic *feleks, *feliks, likely from Proto-Indo-European *bʰel- (“henbane”) + -ix, a suffix akin to -ex found in other plant names (compare cārex (“sedge”), rumex (“sorrel”)). De Vaan posits that -ix is early, not a result of vowel assimilation at the Latin stage. Cognate to Welsh bele, Russian белена́ (belená), Czech blín, Middle Dutch bilse, Old English belene, German Bilsenkraut all meaning "henbane"; henbane stems are feathered like fern leaves, and both plants have medicinal properties.