There are 20 8-letter words that start with 'hydr'.
| hydracid | hydragog | hydranth | hydrants | 
| hydrases | hydrated | hydrates | hydrator | 
| hydrides | hydrilla | hydrogel | hydrogen | 
| hydroids | hydromel | hydronic | hydropic | 
| hydropsy | hydroski | hydrosol | hydroxyl | 
Note: These 20 8-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)