There are 10 7-letter words that start with 'hydr'.
| hydrant | hydrase | hydrate | hydriae | 
| hydride | hydrids | hydroid | hydrops | 
| hydrous | hydroxy | ||
Note: These 10 7-letter words that start with 'hydr' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with hydro, hydra, hydri.
5-letter words start with 'hydr' (2)