Mammoth Uncensored Word List:
18 - 16 letter words starting with q

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