There are 12 words that start with 'opal'.
| opal | opals | opaline | 
| opalesce | opalines | opalesced | 
| opalesces | opalescent | opalescing | 
| opalescence | opalescences | opalescently | 
Note: These 12 words that start with 'opal' are found from the USA & Canada version of the tournament Scrabble word list.