pentapeptide

The story

1. Proto-Indo-European*pénkʷe
2. Proto-Hellenic*pénkʷe
3. Ancient Greekπέντε (pénte)
4. Ancient Greekπεντᾰ- (pentă-)
5. Englishpenta-
6. Proto-Indo-European*pekʷ-
7. Proto-Indo-European*pékʷ-ye-
8. Proto-Hellenic*pét͏̌t͏̌ō
9. Ancient Greekπέσσω (péssō)bf.
10. Ancient Greekπέπτω (péptō)
11. Ancient Greekπεπτόν (peptón)
12. GermanPepton
13. Englishpeptone
14. Proto-Indo-European*dʰeh₁-
15. GermanPepton
16. GermanPeptid
17. Englishpeptide
18. English todaypentapeptide

From penta- + peptide.