monopotassium

The story

1. Ancient Greekμόνος (mónos)
2. Ancient Greekμονο- (mono-)
3. Englishmono-
4. Proto-Germanic*puttaz
5. Frankish*pott
6. Old Dutch*pot
7. Middle Dutchpot
8. Dutchpot
9. Proto-Indo-European*h₂eHs-der.?
10. Proto-Germanic*askǭ
11. Proto-West Germanic*askā
12. Old Dutch*aska
13. Middle Dutchasche
14. Dutchas
15. Dutchpotas
16. Dutchpotasch
17. Englishpotassa
18. Englishpotassium
19. English todaymonopotassium

From mono- + potassium.