There are 18 words that start with 'fatt'.
| fatty | fatted | fatten | 
| fatter | fattens | fattest | 
| fattier | fatties | fattily | 
| fatting | fattish | fattened | 
| fattener | fattiest | fatteners | 
| fattening | fattiness | fattinesses | 
Note: These 18 words that start with 'fatt' are found from the USA & Canada version of the tournament Scrabble word list.