Au pluriel, ce mot se prononce comme au singulier.

Au is the contraction of à + le, so au pluriel literally means in the plural or when it is plural.

French often uses:

• au singulier = in the singular
• au pluriel = in the plural

So this phrase is not describing a place; it is describing a grammatical form.

In French, the usual fixed expressions are:

• au singulier
• au pluriel

You simply learn them as standard grammatical phrases. English speakers may expect in the plural, and French expresses that with au pluriel.

French uses:

• ce before most masculine singular nouns
• cet before a masculine singular noun that begins with a vowel sound
• cette for feminine singular nouns

Since mot starts with the consonant sound m, French uses ce:

• ce mot = this word

If the noun began with a vowel sound, you would get cet instead, as in cet arbre.

Se prononce comes from se prononcer, which here means to be pronounced.

French often uses a reflexive structure where English would use a passive:

• Ça se dit... = That is said...
• Ça se prononce... = That is pronounced...

So:

• ce mot se prononce... literally looks like this word pronounces itself
• but in natural English it means this word is pronounced...

This is a very common French pattern.

Comme means like or as.
Here, comme au singulier means as in the singular or the same way as in the singular.

French is comparing two grammatical situations:

• the plural form
• the singular form

So the sentence means that the pronunciation in the plural is the same as the pronunciation in the singular.

Yes, in a way. French is being concise.

A fuller version could be understood as something like:

• Au pluriel, ce mot se prononce comme il se prononce au singulier.

But French naturally leaves out the repeated part because it is obvious from context. English does this too sometimes.

It sets the context first: as for the plural form...

French often puts this kind of phrase at the beginning to frame the statement. The comma helps mark that introductory phrase.

So the structure is:

• Au pluriel, = In the plural,
• ce mot = this word
• se prononce = is pronounced
• comme au singulier = as in the singular

It is a very natural word order in explanations, dictionaries, and grammar notes.

Here they function like nouns referring to grammatical categories:

• le singulier = the singular
• le pluriel = the plural

Even though singulier and pluriel can also be adjectives, in this sentence they are being used as nouns inside the expressions au singulier and au pluriel.

Yes, very often that is exactly the point of this kind of sentence.

In French, a word may have a different written plural form but sound the same when spoken. A note like this tells the learner that although the word becomes plural in writing, its pronunciation stays the same as in the singular.

Not naturally in this context. For grammatical explanations, French normally says:

• au pluriel
• au singulier

Using dans le pluriel would sound odd here. It is not the standard way to talk about grammatical number.

A more word-for-word version would be:

In the plural, this word is pronounced as in the singular.

That is close to the French structure:

• Au pluriel = In the plural
• ce mot = this word
• se prononce = is pronounced
• comme au singulier = as in the singular

It is very commonly used that way, especially in explanations about words, letters, and sounds.

Examples:

• Cette lettre se prononce... = This letter is pronounced...
• Ce nom se prononce... = This name is pronounced...
• Comment ça se prononce ? = How is that pronounced?

So this sentence uses a very common and useful French pattern.