cycloalkene

The story

1. Proto-Indo-European*kʷelh₁-redup.
2. Proto-Indo-European*kʷékʷlos
3. Proto-Hellenic*kʷókʷlos
4. Proto-Hellenic*kúklos
5. Ancient Greekκύκλος (kúklos)
6. Late Latincyclus
7. Middle Englishcicle
8. Englishcycle
9. Ancient Greekκύκλος (kúklos)
10. Ancient Greekκυκλῐκός (kuklĭkós)
11. Classical Latincyclicu
12. Middle Frenchcyclique
13. Frenchcyclique
14. Classical Latincyclicus
15. Englishcyclic
16. Englishcyclo-
17. Englishalkene
18. English todaycycloalkene

From cyclo- + alkene.