turnest

The story

1. Proto-Indo-European*terh₁-
2. Proto-Indo-European*tórh₁nos
3. Proto-Hellenic*tórnos
4. Ancient Greekτόρνος (tórnos)
5. Latintornus
6. Latintornō
7. Proto-West Germanic*turnēn
8. Old Englishturnian
9. Latintornō
10. Old Frenchtorner
11. Middle Englishturnen
12. Englishturn
13. English todayturnest

From turn + -est.