The story
- Proto-Indo-European*né
- Proto-Indo-European*n̥-
- Proto-Italic*n̥-
- Latinin-
- Middle Englishin-
- Englishir-
- Old Frenchreduire
- Middle Englishreducen
- Englishreduce
- Englishreducible
- Englishirreducible
- Proto-Indo-European*leyg-
- Proto-Germanic*līką
- English todayirreducibly
From irreducible + -ly.
Etymology from Wiktionary, CC BY-SA 4.0.