The word 'nothing' symbolically represents nothing-in-itself. But how can we refer to something that by definition is not there?
To make this clearer: the word 'horse' refers to an actual living horse.
we may take an alternate tack and consider the empty set. This also refers to 'nothing' but in the sense of mathematics, which is not in the sense of philosophy.
To make this clear - note that mathematics is structural, so we identify things by what it is that they do. In this sense, the empty set is defined by what it does with other sets - nothing.
But Nothingness-in-itself or to use Parmenides language, the Void, does no such thing - as it 'is not'