There are 16 words that start with 'cumu'.
| cumuli | cumulus |
| cumulate | cumulous |
| cumulated | cumulates |
| cumulating | cumulation |
| cumulative | cumuliform |
| cumulations | cumulonimbi |
| cumulatively | cumulonimbus |
| cumulativeness | cumulonimbuses |
Note: These 16 words that start with 'cumu' are found from the USA & Canada version of the tournament Scrabble word list.