armchair

The story

1. Proto-Indo-European*h₂er-
2. Proto-Indo-European*h₂érmos
3. Proto-Germanic*armaz
4. Proto-West Germanic*arm
5. Old Englishearm
6. Middle Englisharm
7. Englisharm
8. Proto-Indo-European*ḱe?
9. Proto-Indo-European*ḱóm
10. Proto-Indo-European*ḱm̥-th₂der.?
11. Proto-Hellenic*kətá
12. Ancient Greekκατά (katá)
13. Proto-Indo-European*sed-
14. Proto-Indo-European*sedreh₂
15. Proto-Hellenic*hédrā
16. Ancient Greekἕδρα (hédra)
17. Ancient Greekκᾰθέδρᾱ (kăthédrā)
18. Latincathedra
19. Old Frenchchaiere
20. Middle Englishchayere
21. Englishchair
22. English todayarmchair

From arm + chair.