The story
- Proto-Indo-European*gʷʰiH-(s-)lo-
- Proto-Italic*fī(s)lom
- Latinfīlum
- Late Latinfīlō
- Medieval Latinfīlāmentum
- Englishfilament
- Proto-Indo-European*h₃ed-
- Proto-Indo-European*h₃édosder.?
- Englishfilamentous
- Proto-Indo-European*leyg-
- Proto-Germanic*līką
- English todayfilamentously
From filamentous + -ly.
Etymology from Wiktionary, CC BY-SA 4.0.