Mammoth Uncensored Word List:
18 words ending with ts, 20 letters long

anticonservationists antifluoridationists antiinsurrectionists chemicophysiologists chemostratigraphists cyclostratigraphists electrometallurgists electrophysiologists lithostratigraphists micropaleontologists neuropharmacologists palaeoclimatologists paleoanthropologists paleotempestologists representationalists transformationalists ultrasegregationists ultratraditionalists