Free — with nothing holding you back, no rules, no limits, no one controlling you. Fetters were the iron chains put on a prisoner's ankles, so to unfetter is literally to strike the chains off. That old picture is still doing the work: unfettered is not gentle freedom, it is freedom that used to be chained. You meet it in a fairly narrow set of places, and they are mostly serious: unfettered access, unfettered power, unfettered freedom of speech, unfettered capitalism, unfettered discretion (a legal phrase meaning an official may decide however they like, with no rule above them). Notice that the word can lean either way. "Unfettered access to the archive" sounds good. "Unfettered power" sounds frightening. The word itself is neutral about whether the freedom is wise — it only tells you that nothing is restraining it, and the writer usually leaves you to judge. It belongs to journalism, law, and political argument; you will not hear it at dinner. In grammar it works as an adjective, though it is really the past form of a verb, fetter, that almost nobody uses any more except in this negative form.