If "illegal" is typically used for criminal law, what adjective or adjectives are generally used for breaking civil law?
The term "illegal" is also often used for actions that the law prohibits, but that give rise to civil liability, rather than criminal prosecution. We see such use a lot in questions on Law.SE. One also says that a person "is liable" when there are grounds for a civil suit against that person. One might also say that such a person "has commited a tort" or "has civil liability" or "could be held liable". In the specific cases of copyright, trademark, and patent law, one says that a violator "his infringed" or has committed infringement" and that an act contrary to those laws "is an infringement".
“Illegal” is not limited to criminal matters
Illegal and unlawful are synonymous and refer to any conduct which is in breach of any law. So:
- Murder is illegal and a crime
- Stopping in a No Stopping zone is illegal and a civil offence
- Breaking a contract is illegal and exposes the breacher to civil damages
Tortious might be an adjective you could use. The word essentially means a civil violation (although in a strict legal definition, I believe there also need to be some kind of proveable damages).
I usually only see it in the phrase "tortious interference", but I suspect a legal audience at least would understand its meaning alone.
In the comments to the question, the OP talks about immigration law. US immigration law uses the terms lawful and unlawful to encompass both criminal, civil, and regulatory aspects of immigration law.
This includes immigration violations where there isn't an intent to immigrate. For example, somebody can be "unlawfully present" when they overstay their visa by accident. If you called it "illegal immigrant", you can imply an intent to immigrate.
Similarly, if you hold a green card, you're a "lawful permanent resident".