In his Liberty and Freedom: A Visual History of America's Founding Ideas, David H Fischer calls attention to etymological differences between "liberty" and "freedom" ("Introduction", pp 4-5).
Features in Common
Consider the two leading terms in English usage: liberty and freedom. In early uses, both words implied a power of choice, an ability to exercise one's will, and a condition that was different from slavery. In all those ways, liberty and freedom meant the same thing.
But in other ways their original meanings were different.
Our English word liberty comes from the Latin libertas and its adjective liber, which meant unbounded, unrestricted, and released from restraint. A synonym was solutus, from the verb solvo, to loosen a set of bonds. These words were similar to the Greek eleutheria and eleutheros, which also meant the condition of being independent, separate, and distinct. The Greeks used these terms to describe autonomous cities, independent tribes, and individuals who were not ruled by another's will. ...
Freedom has another origin. It derives from a large family of ancient languages in northern Europe. The English word free is related to the Norse fri, the German frei, the Dutch vrij, the Flemish vrig, the Celtic rheidd, and the Welsh rhydd. These words share an unexpected root. They descend from the Indo-European priya or riya, which meant dear or beloved.The English words freedom and free have the same root as friend, as do their German cousins frei and Freund. Free meant someone who was joined to a tribe of free people by ties of kinship and rights of belonging.
... [T]he original meanings of freedom and liberty were not merely different but opposed. Liberty meant separation. Freedom implied connection. A person with libertas in Rome ... had been granted some degree of autonomy, unlike a slave. A person who had freiheit in northern Europe ... was united by kinship or affection to a tribe or family of free people, unlike a slave.
... A leading scholar concludes that "the Romans conceived of libertas as an acquired civil right, not as an innate right of man."
...[A]nother difference between freedom and liberty. The freeborn people of northern Europe were alike in their birthright of freedom...
In ancient Rome, liberty implied inequality. People were granted different liberties according to their condition.
[excerpted from David H. Fischer. Liberty and Freedom: A Visual History of America's Founding Ideas. Oxford. 2005. Emphasis in original.]