-tirelin

The story

1. Proto-Indo-European*dʰwer-
2. Proto-Hellenic*tʰurā
3. Ancient Greekθῠ́ρᾱ (thŭ́rā)
4. Ancient Greekθῠρεός (thŭreós)
5. Proto-Indo-European*weyd-
6. Proto-Indo-European*wéydos
7. Proto-Hellenic*wéidos
8. Ancient Greekεἶδος (eîdos)
9. Ancient Greekθῠρεοειδής (thŭreoeidḗs)
10. New Latinthyreoīdēs
11. Englishthyroid
12. Englishthyro-
13. Proto-Indo-European*trep-
14. Ancient Greekτρέπω (trépō)
15. Ancient Greekτροπή (tropḗ)
16. Ancient Greekτροπῐκός (tropĭkós)
17. Englishthyrotropin
18. Proto-Italic*wre-
19. Latinre-
20. Old Frenchre-
21. Proto-Indo-European*(s)leg-
22. Proto-Indo-European*(s)leg-s-ós
23. Latinlaxus
24. Latinlaxō
25. Vulgar Latin*laxicāre
26. Vulgar Latin*lassicāre
27. Old Frenchlaschier
28. Old Frenchrelaschier
29. Old Frenchrelaisser
30. Middle Englishrelesen
31. Englishrelease
32. English today-tirelin

From thy(rotropin) + -relin (“pituitary hormone release–stimulating peptide”).