There are 31 9-letter words that start with 'mas'.
Note: These 31 9-letter words that start with 'mas' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with mast, mass, masc, maso, mash, mask, masq, masa, mase, masj, masu.
4-letter words start with 'mas' (5)