diethylene

The story

1. Proto-Indo-European*dwóh₁
2. Proto-Indo-European*dwi-
3. Proto-Hellenic*dwi-
4. Ancient Greekδῐ- (dĭ-)
5. Latindi-
6. Englishdi-
7. Proto-Indo-European*h₂eydʰ-
8. Proto-Hellenic*áitʰō
9. Ancient Greekαἴθω (aíthō)
10. Ancient Greekᾱ̓ήρ (āḗr)influ.?
11. Ancient Greekαἰθήρ (aithḗr)
12. Latinaethēr
13. GermanÄther
14. GermanEther
15. Proto-Indo-European*swel-der.?
16. Ancient Greekῡ̔́λη (hū́lē)
17. GermanEthy
18. Englishethyl
19. Englisheth-
20. Ancient Greekῡ̔́λη (hū́lē)
21. Englishethylene
22. English todaydiethylene

From di- + ethylene.