they are synonyms but liberty is more formal and therefore is used a bit differently.
Almost every constitutions mentions Individual Liberties so liberty is individual and freedom refers to country or land. I am sure some will disagree;-) here.
"I am not at liberty"- it is very common use of liberty, a kind of stock phrase.
We usually say "I am free", not "I have freedom".
Students at school are at liberty to leave for lunch (formal)
Students at scholl are free to leave for lunch (informal)
We say "feel free" to do something" not "be at liberty"
"Our liberty and our freedom is at stake", :shock:what does it mean? Is "liberty" redundant here or perhaps "freedom"?:-? In my opinion, it means: Our Individual Liberties and Freedom of Our country is at stake.
As for your question if liberty derives from French- I have no clue. I would say it has Latin roots rather. But do not take it for granted. Check it with someone.;-)
If we take the definition of arrest to be " taking someone's liberty to answer an alleged offence. We can understand that they are no longer free and they have their freedom stricted but it is their liberty i.e. their ability to act freely that is taken.
I think banderas has given the correct interpretation in bringing about the distinction between ‘freedom’ and 'liberty'. I only like to add that while freedom confers some specific privileges ( such as; freedom of speech, freedom of movement etc), liberty confers an individual the right to act (such as; He is at liberty to reveal the official information.)