Dupondius subaeratus est.

Dupondius is a masculine nominative singular noun of the second declension.

In this sentence, it is the subject:

• dupondius = the thing being talked about

The ending -us is a very common nominative singular ending for second-declension masculine nouns.

Subaeratus is best understood here as an adjective or an adjectival participle.

Grammatically, it is:

• masculine
• nominative
• singular

It matches dupondius in gender, number, and case. That matching is called agreement.

You could look it up in a dictionary as something like subaeratus, -a, -um.

Because it must agree with dupondius.

Since dupondius is:

• masculine
• nominative
• singular

the describing word must also be:

• masculine
• nominative
• singular

So Latin uses subaeratus, not subaerata or subaeratum.

This is a very common Latin pattern:

• servus bonus est = the slave is good
• templum bonum est = the temple is good

The adjective changes form to match the noun it describes.

Est is the 3rd person singular present indicative of sum, meaning is.

It links the subject to the description:

• Dupondius = subject
• subaeratus = description
• est = is

So the structure is:

subject + predicate adjective/participle + form of sum

This is one of the most basic Latin sentence patterns.

Good question. Grammatically, a perfect passive participle + est can form the perfect passive:

• laudatus est = he has been praised

But in many sentences, the participle is felt more like an adjective describing a state:

• ornatus est can mean he is adorned
• clausa est can mean it is closed

So with subaeratus est, the exact nuance depends on context:

• it can be read as a state/description
• or, less adjectivally, as a resulting passive

In a short label-like sentence such as this one, learners will often understand it most naturally as a description of what the dupondius is like.

Because Latin normally has no articles.

So dupondius can mean:

• a dupondius
• the dupondius

Which one is meant depends on the context, not on a separate word like English a or the.

This is normal in Latin and something English speakers have to get used to.

No. Latin word order is fairly flexible.

This sentence uses a very straightforward order:

• Dupondius = subject
• subaeratus = description
• est = verb

But Latin could rearrange the words for emphasis, style, or rhythm. For example, forms like these are possible in principle:

• Subaeratus est dupondius
• Dupondius est subaeratus

The basic meaning would stay the same, though the emphasis might shift.

Also, placing est at the end is extremely common in Latin prose.

Yes. It is a complete sentence.

It has everything it needs:

• a subject: dupondius
• a predicate word describing the subject: subaeratus
• a finite verb: est

So this is a full Latin statement, not just a phrase.

A simple parse would be:

• Dupondius — noun, masculine nominative singular, subject
• subaeratus — adjective / participle, masculine nominative singular, agrees with dupondius
• est — verb, 3rd person singular present indicative of sum

Syntactically, the sentence is:

subject + predicate adjective (or participle) + copula

In a classical-style pronunciation, roughly:

du-PON-di-us su-BAE-ra-tus est

A few helpful notes:

• dupondius has the stress on PON
• subaeratus has the stress on BAE
• ae is pronounced like the vowel sound in aisle or eye
• est is short and crisp

So a rough English approximation is:

doo-PON-dee-oos soo-BYE-ra-toos est

That is only approximate, but it is close enough for a beginner.