Cum pluvia tandem desierit, exeamus e porticu et per vicum ad domum revertamur.

Here cum means when and introduces a temporal subordinate clause:

• Cum pluvia tandem desierit = When the rain has finally stopped

A learner may know that cum can also mean since or although, but here the context clearly shows time: first the rain stops, then the speaker proposes going out and returning home.

Because the stopping of the rain is presented as something that must be completed before the other actions happen.

So the sense is:

• first: the rain stops
• then: let us go out and let us return home

That is why Latin uses desierit, which here has the force of future perfect:

• desierit = will have stopped / has stopped in a future-time setting

If Latin used desinit (is stopping / stops) or desiit (stopped), the timing would feel different.

Formally, desierit can be either:

• future perfect indicative
• perfect subjunctive

In this sentence, the natural understanding is future perfect: when the rain has finally stopped.

Why? Because the main clause is a forward-looking suggestion:

• exeamus = let us go out
• revertamur = let us return

So desierit fits the idea of an action completed before those future actions.

Because pluvia is the subject of desierit.

So the grammar is:

• pluvia = the rain
• desierit = has stopped / will have stopped

Literally, the rain will have ceased.

English often says the rain stops, and Latin can do the same with pluvia as the subject.

They are hortatory subjunctives in the first person plural.

This is how Latin says:

• let us go out
• let us return
• more naturally in English, let's go out ... and let's return

So:

• exeamus = let us go out
• revertamur = let us return

This use is very common when the speaker includes himself or herself in the action.

Because revertor is a deponent verb.

A deponent verb:

• has passive forms
• but an active meaning

So although revertamur looks passive in form, it means:

• let us return

not

• let us be returned

That is completely normal for deponent verbs in Latin.

E and ex are two forms of the same preposition, meaning out of or from.

In practice:

• e is often used before consonants
• ex is often used before vowels, and sometimes before consonants too

So e porticu is perfectly normal and means:

• out of the portico / porch / colonnade

Latin often has this kind of small variation in prepositional form.

Porticu is ablative singular.

That is because e/ex takes the ablative.

So:

• e porticu = out of the portico

Also, porticus is a fourth-declension noun, so its ablative singular is porticu.

They are accusative for two different but related reasons:

• per vicum: per always takes the accusative
• ad domum: ad also takes the accusative

So:

• per vicum = through the street / along the street
• ad domum = to the house / toward home

Both prepositions express movement, and both govern the accusative.

Yes, that is a good question.

Latin very often uses domum by itself to mean homeward / home:

• domum ire = to go home

But ad domum is also possible, especially if the idea is more literally to the house or if the writer wants the destination stated with a preposition.

So:

• domum = very idiomatic home
• ad domum = more explicitly to the house / to home

In this sentence, ad domum is understandable and straightforward.

Tandem means at last, finally, or after all this time.

It adds a feeling of relief or impatience:

• Cum pluvia tandem desierit = When the rain has finally stopped

So the speaker is not just waiting for the rain to stop, but waiting for it to stop at last.

Latin word order is much freer than English word order.

This sentence begins with the cum-clause:

• Cum pluvia tandem desierit

That puts the time-setting first: once the rain has stopped...

Then the main idea comes:

• exeamus ... revertamur

This is a very natural Latin way to organize the sentence:

1. set the circumstances
2. give the proposed action

So the order is not random; it helps the sentence flow logically.

Because the speaker is proposing two coordinated actions:

• exeamus e porticu = let us go out of the portico
• et per vicum ad domum revertamur = and let us return home through the street

Latin often repeats the finite verb in each part rather than making one depend on the other.

So the structure is:

• let us go out
• and let us return

That makes both actions equally clear and deliberate.