There are 17 words that start with 'exon'.
| exon | exons | exonic | 
| exonym | exonyms | exonumia | 
| exonerate | exonumist | exonerated | 
| exonerates | exonumists | exonerating | 
| exoneration | exonerative | exonuclease | 
| exonerations | exonucleases | |
Note: These 17 words that start with 'exon' are found from the USA & Canada version of the tournament Scrabble word list.