There are 15 words that start with 'thei'.
| thein | their | theine |
| theins | theirs | theism |
| theist | theines | theisms |
| theists | theistic | theirself |
| theistical | theirselves | theistically |
Note: These 15 words that start with 'thei' are found from the USA & Canada version of the tournament Scrabble word list.