There are 12 words that start with 'leth'.
| lethe | lethal | 
| lethes | lethals | 
| lethean | lethally | 
| lethargy | lethality | 
| lethargic | lethargies | 
| lethalities | lethargically | 
Note: These 12 words that start with 'leth' are found from the USA & Canada version of the tournament Scrabble word list.