There are 19 13-letter words that start with 'deco'.
Note: These 19 13-letter words that start with 'deco' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with decon, decol, decom, decor, decou, decoc, decod, decoy, decos.
5-letter words start with 'deco' (3)