Mammoth Uncensored Word List:
24 - 18 letter words starting with de

deconstructionists decriminalisations decriminalizations dedifferentiations dehydrochlorinases dehydrochlorinated dehydrochlorinates dehydrogenizations deinstitutionalise deinstitutionalize deliberativenesses dematerialisations dematerializations demythologizations denationalisations denationalizations dendrochronologies dendrochronologist denominationalisms deoxyribonucleases depersonalizations dephosphorylations determinablenesses dextroamphetamines