Postridie vicinae matri gratulantur, quod maritus salvus rediit.

Postridie means the next day or on the following day.

It is an adverb, not a noun, so it does not change its ending for case. It simply tells you when the action happened.

So:

• postridie = the next day
• it modifies the whole main action: gratulantur

This is a very natural question, because vicinae is form-wise ambiguous.

It can be understood as:

• nominative plural of vicina = the female neighbors
• or a form that could go with matri and mean to the neighboring mother

In this sentence, the usual textbook reading is:

• vicinae = the neighbors (subject)
• matri = to the mother (dative)

So the structure is:

• vicinae = the neighbors
• matri = to the mother
• gratulantur = congratulate

In other words: The next day the neighbors congratulate the mother...

A learner notices the ambiguity because Latin endings often allow more than one possibility at first sight. That is completely normal.

Because the verb gratulor takes the dative of the person being congratulated.

So Latin says, literally, something like:

• they congratulate to the mother

That sounds strange in English, but in Latin it is the normal construction.

So:

• matri = to the mother / the mother as the person receiving the congratulations
• case: dative singular

This is a very common thing to remember with vocabulary: some Latin verbs do not take a direct object the way their English translations do.

Because gratulor, gratulari, gratulatus sum is a deponent verb.

Deponent verbs:

• have passive forms
• but active meanings

So gratulantur looks passive because of -ntur, but it means:

• they congratulate
• not they are congratulated

This is one of the most important patterns for learners to get used to in Latin.

Gratulantur is third person plural.

That means:

• they congratulate

The ending -ntur tells you both:

• it is a deponent/passive-form verb
• it is plural

That matches the subject vicinae if we take it as the neighbors.

Here quod means because and introduces a clause giving the reason.

So:

• quod maritus salvus rediit = because the husband returned safe

This is a causal clause.

Latin often uses quod or quia for because. In a sentence like this, quod is simply giving the reason for the congratulations.

The subject of rediit is maritus.

So in the clause:

• maritus salvus rediit

the basic structure is:

• maritus = husband
• rediit = returned
• salvus = safe

So it means the husband returned safe.

Because salvus describes the husband, not the action itself.

It agrees with maritus:

• maritus = masculine singular nominative
• salvus = masculine singular nominative

So salvus is a predicate adjective meaning:

• the husband returned safe
• or more naturally in English, the husband returned safely / returned safe and sound

Latin often uses an adjective where English might prefer an adverbial expression.

Rediit is perfect tense of redeo.

Here it means:

• returned
• or has returned, depending on context

So maritus salvus rediit means that the return has already happened, and that is why the neighbors are now congratulating the mother.

Latin often leaves out possessive words like his, her, or their when the possessor is obvious from the context.

So maritus by itself can mean:

• the husband
• and in context, naturally her husband

Latin does not need to say her husband every time if it is already clear whose husband is meant.

It may feel unusual to an English speaker, but it is perfectly normal Latin.

The sentence begins with the time word:

• Postridie = The next day

Then comes the main clause:

• vicinae matri gratulantur

Then the reason clause:

• quod maritus salvus rediit

Latin word order is much more flexible than English word order because the endings show the grammatical relationships.

So instead of relying mainly on position, Latin relies heavily on:

• case endings
• verb endings
• agreement

That is why you should read by endings first, not by English word order expectations.