There are 18 12-letter words that end with 'tness'.
Note: These 18 12-letter words that end with 'tness' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words end with ntness, ctness, rtness, stness, htness, itness, etness, ptness, atness, ftness, utness, ltness, otness.
7-letter words end with 'tness' (7)