Illegalness refers to the quality or state of being unlawful or prohibited by law. If you are looking for synonyms for the word illegalness, you may want to consider other words that refer to the same concept. Some possible synonyms for illegalness include illegality, lawlessness, criminality, and unlawfulness. Other related words might include non-compliance, contravention, infringement, violation, or transgression. Ultimately, the choice of synonym will depend on the context and intended meaning of the sentence. It is always important to choose the right words to ensure that your message is clear and accurate.