There are 18 words that start with 'ostrac'.
| ostraca | ostracod | ostracon |
| ostracise | ostracism | ostracize |
| ostracode | ostracods | ostracised |
| ostracises | ostracisms | ostracized |
| ostracizes | ostracodes | ostracising |
| ostracizing | ostracoderm | ostracoderms |
Note: These 18 words that start with 'ostrac' are found from the USA & Canada version of the tournament Scrabble word list.