أخيرا يصل القطار.

أخيرًا is an adverb meaning finally or at last.

Historically, it comes from the adjective أخير meaning last/final, but in this sentence it is being used adverbially, so English speakers can think of it simply as finally.

In fully vowelled Arabic, it is usually written أخيرًا with fatḥatayn at the end. That ending reflects the common adverbial accusative form in Arabic.

Because Arabic very often uses verb–subject order, especially in straightforward narration.

So:

يصل القطار = the train arrives

This is a very normal Arabic sentence pattern.

Putting أخيرًا first gives extra focus to the idea of finally / at last, so the sentence feels a bit like:

At last, the train arrives.

You could also say القطار يصل in some contexts, but يصل القطار is very natural in Modern Standard Arabic.

The Arabic imperfect tense, here يصل, can cover several meanings depending on context, including:

• arrives
• is arriving
• sometimes a near-future sense like will arrive

With أخيرًا, the sentence often feels like a narrative present: Finally, the train arrives or At last, the train is arriving.

Arabic often uses the present where English might choose different tenses depending on style.

The prefix يـ marks third person masculine singular in the imperfect tense.

Since القطار (the train) is grammatically masculine singular, the verb must match it:

• يصل = he/it arrives

So here يصل القطار literally means the train arrives, with the verb agreeing with القطار.

This is a very common question.

The past-tense verb is وصل (waṣala) = he arrived.
But in the imperfect, it becomes يصل (yaṣilu), not يوصل.

That is because وصل is a weak verb with an initial و. In this type of verb, the initial و often drops in the imperfect form.

So:

• past: وصل
• present/imperfect: يصل

This is something learners simply get used to with a group of common verbs.

A careful pronunciation is:

ʾakhīran yaṣilu al-qiṭāru

A few useful notes:

• أ at the beginning is a glottal stop: ʾa
• خ is the throaty sound like German Bach or Scottish loch
• ص is an emphatic s
• ق is a deep q sound, not an English k
• ط is an emphatic t

If you say the whole sentence smoothly in connected speech, القطار is often heard as l-qiṭāru after the previous word, because the helping vowel at the start of ال drops in the middle of speech.

ال is the Arabic definite article, meaning the.

So:

• قطار = a train / train
• القطار = the train

Since the sentence refers to a specific train, Arabic uses القطار.

It is pronounced fully: al-qiṭār.

That is because ق is a moon letter (حرف قمري), not a sun letter.

So the ل in ال stays audible:

• القطار = al-qiṭār

If the next letter were a sun letter, the ل would assimilate, but that does not happen here.

It would normally be:

أخيرًا يَصِلُ القِطارُ

The endings show the grammar:

• يَصِلُ: the verb is in the indicative, so it takes ـُ
• القِطارُ: the subject is nominative, so it also takes ـُ
• أخيرًا: the adverb appears in the accusative-style adverbial form

In ordinary Arabic writing, these short vowels are usually omitted, so you normally see:

أخيرا يصل القطار

Yes, but the emphasis changes.

For example:

• أخيرًا يصل القطار = Finally, the train arrives
  Focus on finally
• يصل القطار أخيرًا = The train finally arrives / arrives at last
  Also very natural
• القطار يصل أخيرًا = The train arrives at last
  Possible, but more topic-focused or context-dependent

So the original sentence is natural and idiomatic, especially if you want to highlight the relief or delay expressed by أخيرًا.