“Uncopyrightable” is one of the longest words in the English dictionaries that does not repeat any letters

The longest word could be “subdermatoglyphic” – it’s not in any dictionaries but it’s in dermatology journals.

Dermatoglyphics, misconjugatedly, and uncopyrightable, each fifteen letters long, are the longest English words in which no letter appears more than once.

Fourteen letter words with this property are ambidextrously, benzhydroxamic, hydromagnetics, hydropneumatic, pseudomythical, schizotrypanum, sulphogermanic, troublemakings, undiscoverably, and vesiculography.