Adjective or Noun?

Question

In the following sentence

The term Orwellian has evolved into a descriptive of totalitarian and authoritarian practices.

Is the word 'descriptive' a noun or an adjective? Now it is my understanding that practices is a noun and hence descriptive should be an adjective describing that noun but still, there is a bit of confusion especially when this sentence has been written in a different manner in some places like below.

Orwell’s work continues to influence popular and political culture, and the term Orwellian – descriptive of totalitarian or authoritarian social practices – has entered the language together with many of his neologisms, including Big Brother, Thought Police, Room 101, memory hole, newspeak, doublethink, proles, unperson, and thoughtcrime.

Answer 1

Morphologically it is an adjective, as you rightly say, but syntactically it is here used as a noun.

I guess it could be explained through ellipsis, ie there is an omitted term: The term Orwellian has evolved into a descriptive term of totalitarian and authoritarian practices. But then you have two terms, and so for stylistic reasons the second one has been left out.

So, you could still say that descriptive is an adjective, modifying the 'ghost' of the omitted noun term. As English is very flexible with its parts-of-speech, it's kind of both then, and that works fine, even if it seems a bit unusual.