The best replacement for illegal is undocumented.

The best alternatives to illegal are rated as following:
★★★★★  undocumented
★★★★  unlawful
★★★  illicit
★★★  legal
★★★  unethical
★★  legal immigration
★★  criminal
★  legal drugs
★  illegal
★  immoral
★  legal immigrants
★  undocumented immigrants
★  legal abortion
★  not legal
★  ethical
  illegitimate
  marijuana be legal
  legal moonshine
  legal guns
  joe legal
  legal steroids

Your alternative for illegal is not listed? Suggest!
Speaking about illegal, one probably shouldn't forget about downloading music.

Other search terms related to illegal and their ratings are:
★★★★★ downloading music
You have in mind a companion for illegal and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of illegal in all years. Click on graph for more.
illegal
undocumented
unlawful