There are 12 words that start with 'metast'.
| metastable | metastably | 
| metastases | metastasis | 
| metastatic | metastasize | 
| metastasized | metastasizes | 
| metastability | metastasizing | 
| metastatically | metastabilities | 
Note: These 12 words that start with 'metast' are found from the USA & Canada version of the tournament Scrabble word list.