What is the difference between "illicit" and "illegal"? Are they just synonymous? Used in different contexts?
Something illegal is forbidden by law: "It is illegal for motocyclists [sic] not to wear a crash helmet."
If a thing is illicit it is done by someone who knows that it is disallowed by law but that under different circumstances it could be legal: "The crew were involved in the illicit import of brandy"
(it is basically legal to import brandy but not the way they did it).
This is backed up by things like illicit sexual relationship. It's not wrong to have a sexual relationship normally, but it could be "wrong" if you are married, or not yet married, etc. illicit trade is another such example. It's not wrong to trade, unless you do it in the wrong way.
An illegal action only breaks the law. An illicit action breaks ethical or moral standards (and probably the law as well).
- forbidden by law or statute.
- contrary to or forbidden by official rules, regulations, etc.
- not legally permitted or authorized; unlicensed; unlawful.
- disapproved of or not permitted for moral or ethical reasons.
As you see here, illicit can be used to mean illegal, but its second meaning makes all the difference. So if you want to preserve our precious English nuances, choose wisely!
Maybe the best ways to distinguish the two are their etymologies and their uses, which are related.
Illicit < Lat., licere, to permit.
Illegal < Lat., lex, a statutory law (as opposed to natural law, or what have you).
As noted above, illicit is a broader term that often includes a moral or ethical connotation, whereas illegal does not. It might be illegal to open the coolant reservoir on your air conditioner, but nobody thinks it is immoral. Likewise, adultery is often legal - or if illegal, not considered a criminal offense but only a matter of family law should a divorce be sought - but nobody really thinks of adultery as anything but an illicit affair.
The terms are used, relative to each other, differently in different contexts.
In canon law of the Catholic Church, the two words are synonymous, and are opposed to the term invalid. Validity, in such a distinction, has to do with reality, whereas liceity has only to do with permission and regulation. For instance, a layperson may not preach at Mass. Ask any of my friends and they will tell you how preachy I can be. The Church's law does not deny my ability (validity, you might say - what I can do) to preach - it only denies me permission (liceity or legality - what I may) to do so.
In purely legal matters, though, liceity/validity are often the same thing. If a contract is entered into illicitly, it is generally not going to be valid - for instance, most contracts entered into with minors do not have legal validity.
Lastly, in civic affairs, we very often understand there to be a gap in the law when that which is considered to be illicit (certain shady handling of money by politicians, for instance) is still legal.
Imo, I will choose illicit over illegal when the fact that an act that is being carried out in secret is key to my message. I think that comes across stronger than merely calling the action illegal, even tho being illegal is likely to relegate the act "to the shadows." If I don't want to waste the readers' time making that conclusion, it's likely because I want to build upon that - and delve into the consequence of secrecy.
I’ve always seen illegal and illicit the same way as about 10 dictionaries Google showed me just now, except Cambridge and Collins.
That is, illicit has two different meanings: not legally permitted or authorized; unlicensed; unlawful and separately, disapproved of or not permitted for moral or ethical reasons.
I take that to confirm my long view that anything illegal is illicit but not everything illicit need be illegal.