There are 16 words that start with 'lepto'.
| lepton | leptons | 
| leptonic | leptophos | 
| leptosome | leptotene | 
| leptosomes | leptospire | 
| leptotenes | leptophoses | 
| leptospiral | leptospires | 
| leptocephali | leptocephalus | 
| leptospiroses | leptospirosis | 
Note: These 16 words that start with 'lepto' are found from the USA & Canada version of the tournament Scrabble word list.