There are 8 13-letter words that end with 'ening'.
| disheartening | overburdening | 
| rechristening | premoistening | 
| presweetening | straightening | 
| strengthening | unthreatening | 
Note: These 8 13-letter words that end with 'ening' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words end with tening, dening, kening, eening, hening, pening, vening, zening, sening, fening, mening, cening, iening, lening, rening.
7-letter words end with 'ening' (6)