antiatom

The story

1. Proto-Indo-European*h₂ent-
2. Proto-Indo-European*h₂énts
3. Proto-Indo-European*h₂énti
4. Ancient Greekᾰ̓ντῐ́ (ăntĭ́)
5. Ancient Greekἀντι- (anti-)
6. Englishanti-
7. Proto-Indo-European*né
8. Proto-Indo-European*n̥-
9. Proto-Hellenic*ə-
10. Ancient Greekἀ- (a-)
11. Proto-Indo-European*temh₁-
12. Ancient Greekτέμνω (témnō)
13. Ancient Greek*τομός (*tomós)
14. Ancient Greekἄτομος (átomos)
15. Latinatomu
16. Middle Frenchathome
17. Middle Englishattome
18. Englishatom
19. English todayantiatom

From anti- + atom.