There are 6 15-letter words that start with 'extr'.
| extracellularly | extracurricular | 
| extrajudicially | extralinguistic | 
| extraordinarily | extrudabilities | 
Note: These 6 15-letter words that start with 'extr' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with extra, extre, extru, extri, extro.
5-letter words start with 'extr' (1)