There are 26 15-letter words that end with 'dness'.
Note: These 26 15-letter words that end with 'dness' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words end with edness, idness, rdness, ndness, ldness, adness, udness, wdness, ddness, odness.
7-letter words end with 'dness' (6)