The story
- Proto-Indo-European*né
- Proto-Indo-European*n̥-
- Proto-Germanic*un-
- Proto-West Germanic*un-
- Old Englishun-
- Middle Englishun-
- Englishun-
- Englisharticul(ate)
- Englisharticulable
- English todayunarticulable
From un- + articulable.
Etymology from Wiktionary, CC BY-SA 4.0.