Mammoth Uncensored Word List:
26 - 18 letter words starting with di

diastereoisomerism diethylcarbamazine diethylstilbestrol dihydroergotamines dihydronaphthalene dimethylhydrazines dimethyltryptamine diphenylhydantoins disagreeablenesses discomfortableness disconnectednesses disconsolatenesses discontentednesses discourteousnesses discriminabilities disenfranchisement dishonorablenesses disingenuousnesses disintermediations disproportionately disproportionating disproportionation disputatiousnesses disreputablenesses distinguishability diverticulectomies