From French illégalité, equivalent to il- +‎ legality or illegal +‎ -ity.

illegality (countable and uncountable, plural illegalities)

1. (law) the state of being illegal

   Synonyms: lawlessness, illegalness; see also Thesaurus:illegality

   Antonyms: legality; see also Thesaurus:legality

   The criminal was aware of the illegality of his act.

   • 2020, Douglas G. Morris, The Ernst Fraenkel Dilemma, page 208:

     In Fraenkel’s defiance of mortality and professionalism and his skill in navigating the triple state lay part of the origins of his idea of the dual state. He answered the illegality in the Nazi prerogative state with his own commitment to illegality in both the resistance and even the legal system itself.

2. (law, uncountable) a defense to the validity of a contract because it was in violation of the law

   When sued for refusing to pay for services provided by a prostitute, the customer raised the defense of illegality.

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