There are 13 words that start with 'underd'.
| underdo | underdid |
| underdog | underdoes |
| underdogs | underdone |
| underdose | underdoing |
| underdosed | underdoses |
| underdosing | underdrawers |
| underdeveloped | |
Note: These 13 words that start with 'underd' are found from the USA & Canada version of the tournament Scrabble word list.