I always refer to LDOCE for definitions of words. There is additional info on the senses there. That's why I love it. But, I am still deeply confused with these noun classifications; countable uncountable noun and singular noun. For the former, let's take talent and voice for example. They are classified as countable and uncountable nouns there. Question: under what circumstances are they used as countable nouns? For the latter, let's take appetite (desire for food) and faculty (natural ability) for example. They are classified as singular nouns. Question: are such nouns always used as singular nouns regardless of how many kinds are referred to?
The Cambridge Grammar of the Enlgish Language gives this account of the difference in count and non-count conceptualisations (p335):
A count noun denotes a class of individuated entities of the same kind. Boy, for example, denotes the class of boys. The individual entities are atomic in the sense that they cannot be divided into smaller parts of the same kind as the whole. A boy consists of parts - head, arms, legs, etc. - but these parts are not themselves boys.
So, for the first pair of your examples, talent and voice may be used as countable nouns when we are talking about clearly separable talents or voices, but not when we are talking about an atomic - a singular - talent or voice. A person may even have several different voices themselves, if they are for example a voice actor.
In the second pair of examples, the same idea holds true. We often speak of a person's faculties when we are talking about separate natural abilities that they have, like their factulies of reasoning and speech:
There was no time in which I was not in full possession of my faculties.
However when we speak of a singular faculty, it is a natural ability of one sort only:
It was as if some terrible newscaster had possessed my faculty of speech while my mind drifted away.
As for appetites, we may use this as a count noun when we are talking about multiple people or other living things which each have their own separate appetite. But as long as it is limited to an appetite for food, it is hard to imagine a single person having more than one desire for food.
Small boys have such enormous appetites, don't they?
If we interpret it as an appetite for a particular sort of food, however, then a single person might have separate appetites:
My appetite for chocolate is only surpassed by my appetite for meat. Fortunately both of those appetites are kept well sated.
In the end, it all depends on whether or not the word may be conceptualised in one way or the other. Relying on dictionaries to say which are always countable or non-countable, or always singular is likely to produce frustration when you're met with real-world usage.
Taking specific examples is not particularly helpful when discussing the general idea of countability/uncountability.
Nouns are strange things. They resemble Schrödinger’s Cat: a noun is neither countable nor uncountable until it is observed in context.
As guidance, a noun is never uncountable unless it is used in a context that makes it uncountable. So, when you say, “This noun is uncountable.” You should be saying, “In this context, this noun is uncountable.”
There have been many attempts to create criteria that an uncountable noun must have to be an uncountable noun but these often fail as exceptions are found in new contexts. It is important to realise that you should never say “never countable/uncountable.” English does not work like that – it is filled with exceptions.
There are nouns that are
Almost always uncountable (e.g. guidance, advice, furniture, suspense, anger, jewellery, weather); These are strongly uncountable nouns and are made plural and countable only by the prefixing of “pieces /types/sorts/kinds of, etc.” These are better called mass nouns and are concepts and descriptions of groups of similar items: they do not have a real existence. You cannot put your hand on any of them.
More often uncountable (wood); “The house is made of wood.” These are usually made plural and countable by the prefixing of “types/sorts/kinds of” but “Cedar and pine are woods used for making pencils.”
Commonly both countable and uncountable (very common in foodstuffs) Do you want cake? Do you want a cake? Do you want two cakes? Do you want cakes?
More often countable (man) and “There were three men in the field.” But “Man is the most intelligent species.”
Almost always countable knife, dog, tree, house, car, etc.
All singular countable nouns must be preceded by a/an/one/the, or another determiner.
Uncountable nouns are not preceded by “a/an” but may be preceded by the or another determiner (my, that, any, etc) but need not be.
“[The] Advice given to me indicates that we should stop now." / "The thieves took [my] jewellery and gold."
Uncountable nouns: guidance; advice; pollution; jewellery; goods, hostility, sugar, love, <- in these cases, the noun either cannot be, (or is only very rarely, in specialised cases), directly preceded by a/an/one/two, etc.
On the other hand, a plural unqualified countable noun represents an indefinite number:
“There are potatoes in the field.”
Here, potatoes is the plural of a potato. And a/an noun = one example of one noun from among many such nouns.
Thus potatoes = many examples of potatoes. The plural thus expresses “an indefinite number of individual nouns.”
Thus we have
"Wind destroyed the house." -> uncountable - the general phenomenon of “wind”
“The wind destroyed the house” -> uncountable - either a specific wind that has just been referred to, or the general phenomenon of wind of which listener and speaker are aware.
"A wind destroyed the house" -> countable - one example of wind; an unspecified wind; a random wind.
“Winds destroyed the house.” -> countable - several examples of winds; several random winds.
The winds destroyed the house.” -> countable - several examples of the type of wind of which the listener is aware.
This is reflected in the convention “All countable nouns can be qualified by “many” (which reflects numbers) but not “much” (which reflects a quantity/amount), and all uncountable nouns can be qualified by “much” but not “many”.”