Nox obscura puerum timidum terret.

Because nox is in the nominative singular, which is the case normally used for the subject of a sentence.

Even though English relies heavily on word order, Latin relies much more on word endings. Here:

• nox = nominative singular, so it is the subject
• puerum = accusative singular, so it is the direct object

So the sentence means that the dark night is doing the frightening, and the timid boy is the one being frightened.

Puerum is the direct object of terret. It answers the question whom does the night frighten?

The verb terret means frightens or is frightening, and the person or thing directly affected by that action goes into the accusative case.

So:

• nox obscura = the one doing the action
• puerum timidum = the one receiving the action

Because timidum is an adjective modifying puerum, and Latin adjectives must agree with the nouns they describe in:

• gender
• number
• case

Here:

• puerum is masculine singular accusative
• timidum is also masculine singular accusative

That matching tells you that timidum describes puerum, not nox.

Because it describes nox, and nox is a feminine noun.

Just like timidum agrees with puerum, obscura agrees with nox. So obscura is:

• feminine
• singular
• nominative

This shows that it belongs with nox.

Because nox is a third-declension noun, not a first-declension noun.

A beginner often expects feminine nouns to look like puella, but Latin has feminine nouns in several declensions. Nox, noctis is third declension, so its nominative singular form is nox.

So its gender is feminine, but its declension is third declension. Those are two different things.

Terret is:

• third person singular
• present tense
• active voice
• indicative mood

It comes from terreo, terrere, meaning to frighten.

So terret means he/she/it frightens or is frightening. In this sentence, the subject is nox obscura, so the verb is translated as the dark night frightens.

Because the subject, nox obscura, is singular.

In Latin, the verb agrees with its subject in person and number. Since nox is one thing, the verb must be singular: terret, not terrent.

It matters less in Latin than in English.

Latin allows much freer word order because the endings already show the grammatical roles. So these would still mean basically the same thing:

• Nox obscura puerum timidum terret
• Puerum timidum nox obscura terret
• Obscura nox terret puerum timidum

The usual emphasis may change, but the endings still show that:

• nox obscura is the subject
• puerum timidum is the object

No, not in this sentence.

Timidum is masculine accusative singular, while nox is feminine nominative singular. Since adjectives must agree with the nouns they modify, timidum cannot go with nox.

It must go with puerum, because puerum is also masculine accusative singular.

Because Latin does not have articles like English does.

So nox can mean:

• night
• the night
• sometimes even a night

The same is true for puerum:

• boy
• the boy
• a boy

The exact English wording depends on context and on what sounds natural in translation.

Here it is an adjective meaning dark, dim, or gloomy, agreeing with nox.

A learner may connect it with the English word obscure, and that connection is helpful, but in this sentence the most natural sense is simply dark or gloomy night.

Yes. Latin could say:

• Nox puerum terret = The night frightens the boy

Adding obscura and timidum gives more detail:

• what kind of night? dark
• what kind of boy? timid

So the adjectives are not required for grammatical completeness, but they add description.