There are 13 words that start with 'masto'.
| mastoid | mastodon |
| mastoids | mastodons |
| mastodont | mastopexy |
| mastodonic | mastodonts |
| mastoiditis | mastopexies |
| mastoidectomy | mastoiditises |
| mastoidectomies | |
Note: These 13 words that start with 'masto' are found from the USA & Canada version of the tournament Scrabble word list.