extratracheal

The story

1. Proto-Indo-European*h₁éǵʰ
2. Proto-Indo-European*h₁éǵʰs
3. Proto-Indo-European*h₁eǵʰsteros
4. Proto-Italic*eksteros
5. Latinexter
6. Latinextrā
7. Englishextra-
8. Proto-Indo-European*dʰreh₂gʰ-
9. Proto-Indo-European*dʰréh₂gʰus
10. Proto-Hellenic*tʰrākʰús
11. Ancient Greekτρᾱχεῖᾰ (trākheîă)
12. Late Latintrāchīa
13. Medieval Latintrāchēa
14. Englishtrachea
15. Proto-Indo-European*h₂el-
16. Proto-Indo-European*h₂élisder.?
17. Englishtracheal
18. English todayextratracheal

From extra- + tracheal.