There are 18 words that start with 'jump'.
| jump | jumps | jumpy | 
| jumped | jumper | jumpers | 
| jumpier | jumpily | jumping | 
| jumpoff | jumpable | jumpiest | 
| jumpoffs | jumpsuit | jumpiness | 
| jumpingly | jumpsuits | jumpinesses | 
Note: These 18 words that start with 'jump' are found from the USA & Canada version of the tournament Scrabble word list.