illegal
Violating a law; prohibited by law or unlawful.
Das Herunterladen von urheberrechtlich geschützten Filmen ist illegal.
Downloading copyrighted films is illegal.

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Violating a law; prohibited by law or unlawful.
Das Herunterladen von urheberrechtlich geschützten Filmen ist illegal.
Downloading copyrighted films is illegal.

The word consists of the prefix 'il-' and the adjective 'legal' (legal). The prefix 'il-' is a form of the negative prefix 'in-' and is used before words that begin with 'l'. So 'illegal' literally means 'not legal'.
Es ist illegal, ohne Lizenz ein Restaurant zu betreiben.
It is illegal to run a restaurant without a license.
'Illegal' can also be used as an adverb to describe how an action is carried out. It then answers the question 'How?'.
Er hat die Software illegal heruntergeladen.
He downloaded the software illegally.
The word is often used in connection with law and crime. Typical combinations are 'illegale Drogen' (illegal drugs), 'ein illegaler Aufenthalt' (an illegal stay), 'illegale Aktivitäten' (illegal activities), or 'etwas für illegal erklären' (to declare something illegal).
Der Besitz bestimmter Waffen ist in diesem Land illegal.
Possession of certain weapons is illegal in this country.
black
'schwarz' and 'illegal' can both mean that something is not allowed or not officially registered. In this sense, 'schwarz' is colloquial and often appears in fixed expressions, for example for work without registration or riding without a valid ticket. 'illegal' is more general and more neutral; it fits anything that violates a law. The words can be confused because they are similar in some situations. In practice: 'illegal' is the clear, general form, while 'schwarz' sounds more everyday and only fits certain expressions.

Das Kopieren dieser Software ist illegal.
Copying this software is illegal.
Der Handwerker darf nicht schwarz arbeiten, sonst bekommt er Probleme.
The tradesman must not work off the books, or he will get into trouble.