There are 17 words that start with 'exos'.
| exosmic | exosmose | exospore | 
| exosmoses | exosmosis | exosmotic | 
| exosphere | exospores | exosporia | 
| exostoses | exostosis | exospheres | 
| exospheric | exosporium | exoskeletal | 
| exoskeleton | exoskeletons | |
Note: These 17 words that start with 'exos' are found from the USA & Canada version of the tournament Scrabble word list.