There are 15 words that start with 'besti'.
| bestir | bestial | besting | 
| bestirs | bestiary | bestially | 
| bestirred | bestiality | bestialize | 
| bestiaries | bestirring | bestialized | 
| bestializes | bestialities | bestializing | 
Note: These 15 words that start with 'besti' are found from the USA & Canada version of the tournament Scrabble word list.