There are 30 9-letter words that start with 'sin'.
Note: These 30 9-letter words that start with 'sin' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with sing, sinu, sinc, sino, sine, sini, sink, sinf, sint, sinl, sinn, sins, sina, sinh.
4-letter words start with 'sin' (5)