There are 13 words that start with 'regres'.
| regress | regressed | 
| regresses | regressor | 
| regressing | regression | 
| regressive | regressors | 
| regressions | regressively | 
| regressivity | regressiveness | 
| regressivities | |
Note: These 13 words that start with 'regres' are found from the USA & Canada version of the tournament Scrabble word list.