Illicit and Illegal

The samples that have been obtained Illicitly

The samples that have been obtained Illegally

are they equivalents?

PS: should I say "are they equivalent?" or "are they equivalents?"

the "equivalent" here seems correct grammatically whatever in noun or adjective, but which way to use it is more native?

Good question, Cleveland! While both of these adjective MAY be used to describe the same thing, they do not have the same meaning.

"Illegal", of course, means something that violates the law of the land--for example, murder or theft.

"Illicit" refers to an activity that is considered improper or wrong. It can also refer to something that is done "undercover" or "on the black market."

Thus, "illicit drug trade" is also illegal. On the other hand, an "illicit meeting" between cheating lovers may be "undercover" and "improper" (i.e., morally wrong), but not actually illegal.

Hope this helps!