There are 15 15-letter words that start with 'multi'.
Note: These 15 15-letter words that start with 'multi' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with multip, multic, multis, multif, multit, multil, multim, multiv, multib, multie, multin, multid, multir, multia, multig, multih, multiu, multiw, multij, multio, multiy.
8-letter words start with 'multi' (10)