There are 18 words that start with 'ferri'.
| ferric | ferried | 
| ferries | ferrite | 
| ferriage | ferrites | 
| ferritic | ferritin | 
| ferriages | ferritins | 
| ferriferous | ferrimagnet | 
| ferricyanide | ferrimagnets | 
| ferricyanides | ferrimagnetic | 
| ferrimagnetism | ferrimagnetisms | 
Note: These 18 words that start with 'ferri' are found from the USA & Canada version of the tournament Scrabble word list.