There are 12 words that start with 'monst'.
| monster | monstera | 
| monsters | monsteras | 
| monstrous | monstrance | 
| monstrances | monstrosity | 
| monstrously | monstrosities | 
| monstrousness | monstrousnesses | 
Note: These 12 words that start with 'monst' are found from the USA & Canada version of the tournament Scrabble word list.