Mammoth Uncensored Word List:
18 words that are 16 letters long beginning with q in the mammoth uncensored word list.

quadragintillion quadrantectomies quadricentennial quadruplications quantificational quantitativeness quarterfinalists quasicrystalline quasigeostrophic quasiperiodicity questionableness quindecilliardth quingentilliards quingentillionth quinquadecillion quinquesyllables quinquevalencies quintessentially