There are 12 13-letter words that start with 'mer'.
| mercantilisms | mercantilists | 
| mercenariness | mercerization | 
| merchandisers | merchandising | 
| merchandizing | mercilessness | 
| mercurialness | meritocracies | 
| meritoriously | merrythoughts | 
Note: These 12 13-letter words that start with 'mer' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with merc, meri, merr, merg, mero, merl, mere, merm, merb, merd, merk.
4-letter words start with 'mer' (4)