Proscriptio auctionem nuntiat.

• Proscriptio is the subject.
• auctionem is the direct object.
• nuntiat is the verb.

So the sentence has the basic structure subject + object + verb: Proscriptio auctionem nuntiat.

We know from its case.

• proscriptio is nominative singular, the case normally used for the subject.
• auctionem is accusative singular, the case normally used for the direct object.

In Latin, the endings usually tell you what each noun is doing in the sentence more clearly than word order does.

Because it is in the accusative singular.

The accusative is commonly used for the direct object of a verb, the person or thing receiving the action. Here, the thing being announced is auctionem, so it appears in the accusative.

Its dictionary form is auctio, but in this sentence it changes form to auctionem.

nuntiat is a 3rd person singular present active indicative verb form from nuntio, nuntiare.

That means it can be understood as:

• he announces
• she announces
• it announces

Here, since the subject is proscriptio, the natural English rendering is it announces.

The ending -t is the normal marker for 3rd person singular in Latin present tense.

Because Latin does not have articles like English the, a, or an.

So:

• proscriptio can mean the notice or a notice
• auctionem can mean the auction or an auction

English has to choose an article when translating, but Latin leaves that to the context.

No. Latin word order is much more flexible than English word order because the case endings already show the grammatical roles.

So the following could also be grammatical:

• Auctionem proscriptio nuntiat
• Nuntiat proscriptio auctionem

The basic meaning would stay the same, though the emphasis might change. The version you have, with the verb at the end, is a very normal Latin pattern.

They are:

• proscriptio, proscriptionis — a feminine noun
• auctio, auctionis — a feminine noun
• nuntio, nuntiare, nuntiavi, nuntiatum — a verb

For nouns, Latin dictionaries usually give the nominative singular and genitive singular.
For verbs, they usually give the principal parts.

Both are third-declension feminine nouns.

That is why their forms look a little less predictable to an English speaker than first-declension nouns like puella.

For example:

• proscriptio → nominative singular
• proscriptionis → genitive singular
• proscriptionem → accusative singular

and similarly:

• auctio → nominative singular
• auctionis → genitive singular
• auctionem → accusative singular

So auctionem fits a normal third-declension pattern.

Not necessarily.

English proscription usually suggests forbidding, condemnation, or outlawing. But the Latin proscriptio can have a wider range of meanings depending on context, including a public notice, posted announcement, or written advertisement/listing.

In this sentence, because it announces an auction, the sense is clearly something like notice or advertisement, not the modern English sense of proscription.