My brain is broken now. I admit defeat. I do not know what a noun is. My current understanding was a person place or thing and the vocabulary book I'm working through has broken me.
Penurious is an adjective. One could say that a student is penurious. This makes sense.
Penuriousness is a noun. But why? I'm missing a link and it is rattling my brains.
Maybe it would be better to start with a simple word, like good.
Good is an adjective. If we describe something as good, it has features of some kind that make it desirable. But what are those features? Well, it depends what the thing is. Good food is tasty, nutritious, etc. A good person does good things.
A feature is a noun: if we want a noun to describe a good feature, we put -ness on the end of an adjective, and we get goodness.
Penurious is an adjective: if a person has no money, we can say that he or she person is penurious. If we want to talk about the state of having no money, we need a noun: put -ness on the end, and penuriousness is that noun.
Adding -ness isn't always the right thing to do though: the word penury is a noun, and is changed to an adjective by adding the -ous ending to make penurious. So we don't need to adding -ness in this case- we can simply cut some letters off to get back to a noun (penury).
Slippery, for example, is an adjective. It can be used to describe something, such as a surface, on which it is easy to lose your footing, or any thing whose surface has very little friction.
The ball bearing was coated in oil and it was very slippery.
Ice can be very slippery.
We can create a noun that stands for the idea or concept or quality of being slippery by tacking the -ness ending onto the adjective: Slipperyness (usually spelled slipperiness, but that's just an accident of orthography).
This -ness ending can be applied to most adjectives ending in -y- and to many others not ending in -y.
Happy....happiness.
Spicy... spicyness
Tricky....trickiness
Fatty...fattiness
Quaint...quaintness.
Quiet...quietness
Quick....quickness.
Dull....dullness.
Some adjectives are formed from a noun. Penurious is one of them. It comes from the noun penury. It has an adjectival ending, -ous. To turn these adjectives back into nouns, we don't add an ending, rather we remove the ending that turned the noun into an adjective.
You might think of a noun as a physical object, like a car or a book or Brad Pitt. But a noun can also represent a discrete concept (like penury) or a set (or school) of related ideas (like epistemology). Anything that can be called a thing can be a noun, even if you can't point to it.
Many adjectives either derive from the noun forms, or can be converted into nouns. The list is far too long to write out here, but the point is that if we describe something as "enjoyable", that thing should be an object that has or induces a feeling of "enjoyment". The noun will relate to the adjective (and to the verb if one exists, like "enjoy").
In more linguistic terms, nouns can act as the subject or object of a verb in a sentence. I can't say:
Penurious is not fun.
but I can say:
Penury (penuriousness) is not fun.
Nouns can also have properties which can be described by adjectives ("a disagreeable penury", "the beautiful Angelina Jolie") or various grammatical phrases (Angelina Jolie, who is soon to be single).
Although it is perhaps more satisfying to try to define a noun by comprehensively listing what it refers to (person / animal / place / object ...), one soon realises that this is nigh on impossible. Not-exactly-objects-or-places like space, hole, gap, concepts like silence, absence, ownership, dissonance, beliefs, ideologies and fields like Buddhism, nihilism, politics, industry, biology, philately ... are seen to be sufficiently similar to prototypical nouns to warrant including in the class.
Eventually, syntactic (eg can they be used as subjects of sentences) and distributional (eg can a suitable adjective be put before them) considerations are given more weight by serious analysts.
