The story
- Proto-Indo-European*né
- Proto-Indo-European*n̥-
- Proto-Germanic*un-
- Proto-West Germanic*un-
- Old Englishun-
- Middle Englishun-
- Englishun-
- Englishfalter
- Englishfaltering
- Englishunfaltering
- Proto-Indo-European*leyg-
- Proto-Germanic*līką
- English todayunfalteringly
From unfaltering + -ly.
Etymology from Wiktionary, CC BY-SA 4.0.