Mammoth Uncensored Word List:
14 - 18 letter words starting with q

quadragintilliards quadragintillionth quadringentilliard quadringentillions quantificationally quantitativenesses quasiperiodicities quattuordecilliard quattuordecillions questionablenesses quingentilliardths quinquadecillionth quinquagintilliard quinquagintillions