Etsi auspex sero venit, deductio ante noctem incipit.

Etsi introduces a concessive clause. In this sentence, it means although or even though. It signals that the first idea might seem like an obstacle, but the main statement still happens anyway.

So the structure is:

• Etsi auspex sero venit = the concessive clause
• deductio ante noctem incipit = the main clause

Because etsi normally takes the indicative when the speaker is treating the statement as a real fact.

So Latin does not automatically use the subjunctive after a word meaning although. Here the sense is straightforward: the lateness is presented as something real, not hypothetical.

Without macrons, venit can be ambiguous.

• venit = comes or is coming
• vēnit = came or has come

So if the meaning you were shown uses comes, then read it as present. If it uses came, then it is the perfect vēnit.

This is a very common issue in Latin texts printed without macrons.

Because sero is an adverb, while serus is an adjective.

• serus = late as an adjective, as in a late arrival
• sero = late as an adverb, modifying a verb

Here it modifies venit, so Latin uses the adverb: he comes late.

This is one place where English can hide the difference, because late works as both adjective and adverb in English.

Auspex is nominative singular, and it is the subject of venit.

You can tell from the sentence structure:

• auspex = the one doing the coming
• venit = comes/came

It is a third-declension noun. Its dictionary form is auspex, auspicis.

Literally, auspex is someone who observes omens, especially from birds. Depending on context, English may translate it as augur, diviner, or something similar.

In some texts, especially where Roman customs matter, keeping the cultural word auspex or translating it more specifically can be helpful.

Deductio is also nominative singular, so it is the subject of incipit.

The noun literally means a leading away/down/home, but in Roman social context it often refers to a procession or, more specifically, the ceremonial escort of a bride to her new home.

So:

• deductio = the thing that begins
• incipit = begins

Its dictionary form is deductio, deductionis.

Because ante takes the accusative case.

So:

• nox = nominative
• noctem = accusative

That is why Latin says ante noctem.

Here ante is being used temporally, meaning before in time, not location. The phrase can be translated literally as before night, but idiomatically before nightfall is often more natural English.

Because Latin has no articles.

A noun like auspex can mean:

• the augur
• an augur

and deductio can mean:

• the procession
• a procession

English has to choose based on context, but Latin usually does not mark that difference explicitly.

Yes, but not in a strange way. Latin word order is flexible, and this sentence is quite natural.

A few things are worth noticing:

• The etsi clause comes first, which is very common.
• sero is placed near venit, the word it modifies.
• ante noctem comes before incipit, which can give a slight sense of time pressure or emphasis: before night is important.

Because Latin relies heavily on case endings, the sentence could be rearranged in other ways without changing the basic meaning.

Not nearly as much as in English.

In modern printed Latin, the comma helps the reader see the break between the concessive clause and the main clause. But the grammar is really shown by:

• etsi, which marks the subordinate clause
• the verb forms
• the case endings

Ancient Latin writing often had much less punctuation than modern editions do.