Trigger words: Money (2) money
Indicator sentences: Money can be any form of liquid currency. It just so happens that the money you're familiar with is printed by governments but that isn't inherently true of money.
Negotiation parts: Money inevitably emerges in society with or without a legal system because the only alternative is direct bartering which becomes less and less feasible as society grows. There is such a thing as a substance which is understood to have intrinsic value. Gold is an example in many places throughout history. It can be used as a medium of exchange in an abstraction of bartering, in a way that is similar to the use of money. But when it manifests in the form of uniformly crafted objects that are by definition interchangeable with each other, it does so through the mechanism of a legal system. The only possible exception I can think of is cryptocurrency like bitcoin, about which we could have a very interesting but totally irrelevant discussion about whether code is law. But the main take-away is that money has never manifested in a way that was not explicitly within, and built on the context of, a discrete, discernible legal system. Yes, you're right. Bartering becomes unfeasible as society grows. The mechanism by which the increased complexity of society is sustained **is** government. When people in a community collectively agree on sets of rules to all follow (like: all the shiny metal disks stamped with this picture of the emperor's face are interchangeable, but nobody is allowed to forge them without permission) that is governance. That is law. There's no escaping it: literally the difference between money and other media of exchange is that it's regulated by an explicit collective agreement among the group using it -- which is what law is.