Given that there are several senses of 'nothing', we should consider 'nothing' in these different senses.
As A Word
'Nothing' as a word is indeed something. It is a symbol, an utterance, what have you. Now, though it is indeed a something taken as a word in itself, granted that it does not refer to anything, it is seemingly undisputed that unlike words that refer, the word 'nothing' does not contain a positive meaning (granted that it does not have a positive referent).
The meaning of 'nothing' depends wholly on context in other words. We say that there is 'nothing' in light of certain somethings. So we would say that 'there is nothing like a well made strawberry shortcake', where 'nothing' only has meaning in the way that it is used in the sentence, as a way to explicate the satisfaction gained from a well made strawberry shortcake.
As A Metaphysical Consideration
When metaphysicians speak of 'nothing' they typically aren't talking about the word alone, 'nothing'. They're talking about the absence of something. Now, this shouldn't be confused with the absurd suggestion that metaphysicians consider something that is nothing. Just as the word 'nothing' is understood strictly only by context of words that (potentially) have real referents or positive meanings, so too is nothing considered metaphysically only understood in light of that which is real, aka 'something'.
So the very notion of 'nothing' is simply the absence of something.
As A Concept
This is where the trouble starts. Since some philosophers consider 'concepts' as separate mental objects of a Meinongian nature, neither here nor there, 'nothing' is itself taken to be a positive concept.
This confusion can easily be avoided if we readjust our approach to the notion of a concept. Nominalist pragmatists have sought to avoid this problem by postulating the nonexistence of this odd sort of mental stuff, ridding of concepts entirely, restricting all talk of meaning to the way we use our words.
But another solution could be to consider the notion of 'concept' as an action rather than an object. In this analysis, a 'concept' is simply mental activity, the form being comprehended being just whatever is real. That we comprehend 'nothing' has already been found to be possible by the analysis of something, wherein we use peripheral knowledge and imagination to notice the absence of something.
These two differing solutions have their own independent reasons for being favored by philosophers of different breeds and traditions. What is somewhat clear, at least for myself, is that the Meinongian an the modern representative view on semantics in general is failing in quite a few ways, for reasons that your inquiry into nothingness makes clear.