There are 282 12-letter words that start with 'su'.
Note: These 282 12-letter words that start with 'su' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with sub, sup, sur, sul, sun, suc, sum, sus, suf, sug, sud, sui, sua, sut, sue, suk, suz, suq.
3-letter words start with 'su' (7)