echoacoustic

The story

1. Proto-Indo-European*sweh₂gʰ-
2. Proto-Hellenic*wākʰā́
3. Ancient Greekἠχή (ēkhḗ)
4. Ancient Greekἠχώ (ēkhṓ)
5. Latinēchō
6. Medieval Latinēccō
7. Middle Englisheccho
8. Englishecho
9. Proto-Indo-European*h₂eḱ-
10. Proto-Indo-European*h₂ew-
11. Proto-Indo-European*h₂ṓws
12. Proto-Indo-European*h₂ḱh₂owsyéti
13. Proto-Hellenic*akóuhō
14. Ancient Greekἀκούω (akoúō)
15. Ancient Greekᾰ̓κουστῐκός (ăkoustĭkós)
16. Medieval Latinacousticus
17. Englishacoustic
18. English todayechoacoustic

From echo + acoustic.