There are 13 words that start with 'proo'.
| proof | proofs | proofed |
| proofer | proofers | proofing |
| proofread | proofroom | proofreads |
| proofrooms | proofreader | proofreaders |
| proofreading | ||
Note: These 13 words that start with 'proo' are found from the USA & Canada version of the tournament Scrabble word list.