believeth

The story

1. Proto-Indo-European*h₁ep-
2. Proto-Indo-European*h₁éps
3. Proto-Indo-European*h₁épi
4. Proto-Indo-European*h₁pi
5. Proto-Germanic*bi
6. Proto-Germanic*bi-
7. Proto-West Germanic*bi-
8. Proto-Indo-European*lewbʰ-
9. Proto-Germanic*laubō
10. Proto-Germanic*laubijaną
11. Proto-West Germanic*laubijan
12. Proto-West Germanic*bilaubijan
13. Old Englishbelīefan
14. Middle Englishbileven
15. Englishbelieve
16. English todaybelieveth

From believe + -eth.