In "Kant and the platypus", Umberto Eco notes that there is something, before somebody talks about it.
I think that is is exactly and entirely equivalent with limited. A subject can't notice something without perceiving, or inventing, a limit (or attribute) of that something.
The general case is the universe. Here, we invented a name that means all, that is, unlimited; that is, unlimited by any distinctive feature, because it can't be compared to another all.
Therefore all, the universe, includes everything, and, along with it, anything anybody can imagine beyond everything. The only notion equivalent with all is nothing.
Therefore, because any subject/observer is necessarily a part of all/nothing, or a feature of it, it follows that any subject is bound to consider anything noticeable as being, that it is.
So, is means limited, that is, has attributes, that is, can be talked about or indicated, enumerated.
So, I think that is, or can be talked about, or can be described, or can be pointed at, are entirely equivalent and synchronous attributes of a subject's knowledge.
It also follows that the only something which is in itself, independent of any observer's existence, is all (has all the imaginable and unimaginable properties).
And all, the universe, can be, in a simpler manner, denoted as nothing: the all has all the properties and their opposites simultaneously.
If this picture seems unintelligible to you, note that the number 0 (zero) can be represented as a compensating sum of arbitrary integer numbers, but any part of this combination can be said to have a specific attribute, that is, can be said to be.
This picture also implies, as a byproduct, that any subject/observer is compensated for by the rest of the universe, which means, operationally, that no observer can be precisely delimited objectively, that is, any defined observer is a convention among many other observers, or, briefly, there is no unique and local definition of an observer/subject. The same applies to anything that can be said to be.
Therefore a unique and local definition of anything, is, in fact, a belief, a dogma, a convention, a contract; and needs to be interpreted as nothing more than a proposal.
One has the freedom to agree or not with this proposal, but naturally any choice has consequences. And from here comes the criteria we use when making choices: the best choice seems to be the one which also gives you the means to estimate, and check (while you still can do something obvious about it), the consequences you care about. That's one of the reasons why science is preferable to any institutionalized religion.