Hugo Grotius stated that “Justice…denotes nothing but what is just, indeed more in the negative sense than the positive, insofar as justice is that which is not unjust.”
Is this not circular? A tautology of sorts?
Moral language in general is not reducible to non-moral language. You can define justice in various ways using terms like "deserving", "balancing the scales", "setting things right", etc., but then if you try to define those terms you will circle back to justice. However, this doesn't make moral language ill-founded; or rather, it doesn't make moral language any more ill-founded than any other subject matter. You can't define geometric terms without geometric terms, physical terms without physical terms, mental terms without mental terms, etc.
There are many domains of knowledge like this, and the only way to get people to understand each other is to discuss the concepts until they are all using the words in the same way. At that point, you can hope that there is a real meeting of the minds.
Grotius’ definition is indeed circular, and useless. The question is why he did this to himself. In an extended section defining his terms, he never returns to this puzzling position.
After this quote, Grotius continues his analysis of justice and right. Here are the next two sentences of Section 3:
Now any thing is unjust, which is repugnant to the nature of society, established among rational creatures. Thus for instance, to deprive another of what belongs to him, merely for one's own advantage, is repugnant to the law of nature, as Cicero observes in the fifth Chapter of his third book of offices; and, by way of proof, he says that, if the practice were general, all society and intercourse among men must be overturned.
[The Rights of War and Peace, Book 1, chapter 1 (Project Gutenberg)]
This definition, apart from whether one agrees with it, is noncircular.
Grotius’s (noncircular) discussion continues through Section 3, and then through Sections 4 to 17 (the translator omits Section 8). The nonsense definition that opens the section is left an orphan.