Cum imber desierit, iterum procedere poterimus.

Here cum means when.

Latin cum can mean several different things depending on context:

• with as a preposition: cum amico = with a friend
• when as a conjunction of time
• sometimes since or although

In Cum imber desierit, iterum procedere poterimus, it introduces a time clause, so the sense is when the rain has stopped / when the rain stops.

Desierit is the 3rd person singular future perfect indicative of desinere, meaning to stop, cease.

So literally it means:

• desierit = he/she/it will have stopped

Since the subject is imber (rain), the meaning is:

• the rain will have stopped

A very important point for learners: desierit has the same form as the perfect subjunctive, so context matters. In this sentence, because the main verb is future (poterimus) and the meaning is clearly future time, it is understood as future perfect indicative.

Latin often uses the future perfect in a subordinate clause when one future action must be completed before another future action happens.

That is exactly what is happening here:

• first: the rain will stop
• then: we will be able to proceed again

So Latin says, very literally:

• When the rain will have stopped, we will be able to proceed again

Natural English usually does not say that with a future perfect in the when-clause. We usually say:

• When the rain stops, we will be able to proceed again
• or When the rain has stopped, we will be able to proceed again

So the Latin future perfect often matches English present or present perfect in this kind of clause.

Imber is nominative singular.

It is the subject of desierit, because the rain is what is stopping.

So:

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

Even though English often says the rain stops, that is structurally the same idea: rain is the subject.

Because poterimus means we will be able, and verbs like posse normally take an infinitive to complete their meaning.

So:

• poterimus = we will be able
• procedere = to proceed / to move forward

Together:

• procedere poterimus = we will be able to proceed

If the sentence had procedemus, it would mean simply:

• we will proceed

That would remove the idea of ability or possibility.

Procedere literally means to go forward, advance, or proceed.

In this sentence, it probably has the practical sense:

• to move on
• to continue onward
• to proceed with the journey

Because the sentence mentions rain, the idea is likely that travel or movement had been interrupted, and after the rain stops, they can continue.

Iterum means again.

So it shows that the action of going forward had already been happening, then was interrupted, and will resume:

• iterum procedere poterimus = we will be able to proceed again

Without iterum, the sentence would simply mean we will be able to proceed. With iterum, it clearly means resume proceeding.

The word order is natural, but not rigid.

Latin often puts a subordinate clause first, especially a time clause like this:

• Cum imber desierit = When the rain has stopped

Then the main clause follows:

• iterum procedere poterimus = we will be able to proceed again

Within the main clause, procedere comes before poterimus, which is common with an infinitive plus a finite verb, but Latin could vary the order.

For example, these would still be understandable Latin:

• Cum imber desierit, poterimus iterum procedere.
• Iterum poterimus procedere, cum imber desierit.

The original order is simply a smooth and ordinary way to say it.

This is a good question because learners are often told that cum takes the subjunctive.

The full truth is that cum can be used in different ways:

• temporal cum can take the indicative
• circumstantial, causal, or concessive cum often takes the subjunctive

In this sentence, the meaning is straightforwardly temporal: when the rain has stopped. So the verb is understood as future perfect indicative.

What makes this tricky is that desierit looks exactly like a perfect subjunctive form. But the future-time context and the meaning of the sentence show that it is functioning as a future perfect indicative here.

Yes. Both can work.

Latin desierit is more literally will have stopped, which emphasizes completion before the next action. English can express that idea in two natural ways:

• When the rain stops, we will be able to proceed again
• When the rain has stopped, we will be able to proceed again

The second is a little closer to the Latin form, but the first is often the most natural everyday English.