La reunión comenzó tarde.

Because reunión is a feminine noun, so it takes la.

A useful pattern: many nouns ending in -ión are feminine, for example:

• la reunión
• la canción
• la información

So the article and any adjectives would agree in the feminine form when needed.

Comenzó is the third-person singular preterite form of the verb comenzar, meaning to begin or to start.

So here it means:

• he/she/it began
• and with la reunión as the subject, it means the meeting began

This is why the verb ends in -ó: it matches él / ella / usted or any singular noun such as la reunión.

Because comenzó presents the beginning as a completed event in the past.

• comenzó = began / started as a single finished action
• comenzaba = was beginning / used to begin, which gives more of a background, ongoing, or habitual sense

In this sentence, the meeting’s start is treated as one specific event, so comenzó is the natural choice.

Yes. That is completely natural.

empezar and comenzar both mean to start / to begin. In many everyday situations they are interchangeable.

A rough tendency is:

• empezar = often slightly more common in casual speech
• comenzar = sometimes feels a little more formal or polished

But both are very normal, and both would sound correct in Spain.

The written accent shows where the stress goes: reu-nión.

Without getting too technical, Spanish spelling rules say that a word ending in n, s, or a vowel is normally stressed on the second-to-last syllable unless there is a written accent.

Since reunión is stressed on the last syllable, it needs the accent mark:

• reu-nión

It also helps show that the final part is pronounced clearly as -ón.

The accent marks the stress on the last syllable:

• co-men-zó

It also helps distinguish this past-tense form from other forms of the verb.

For example:

• comenzó = he/she/it began
• comenzo without an accent would not be correct Spanish spelling

So the accent is both a pronunciation guide and part of the correct written form.

In most of Spain, z is pronounced like the th in think.

So comenzó sounds approximately like:

• ko-men-THO

More fully, in Spain the sentence is roughly:

• la reu-nyon ko-men-THO TAR-de

A couple of notes:

• z in Spain = English th in think
• c before e or i is also usually that same th sound in Spain
• In much of Latin America, the z would sound more like s

Here, tarde is functioning as an adverb, meaning late.

It tells us how the meeting began:

• comenzó tarde = began late

Even though tarde can also appear in other roles, in this sentence it is not describing the noun reunión directly. It is modifying the verb comenzó.

Because Spanish often does not need an explicit subject pronoun.

The subject here is already stated as la reunión, so there is no need for an extra word like it.

Spanish often avoids dummy subjects that English requires. Compare:

• English: The meeting began late
• Spanish: La reunión comenzó tarde

Also, if the context were clear, Spanish could even drop la reunión and simply say:

• Comenzó tarde

That would mean It began late or The meeting began late, depending on context.

Yes, but La reunión comenzó tarde is the most neutral and standard order.

Other orders are possible, for example:

• Comenzó tarde la reunión

This is grammatically correct, but it sounds more marked or stylistic. It might be used for emphasis, narration, or a particular rhythm.

For learners, the safest default is:

• Subject + verb + adverb
• La reunión comenzó tarde

It could be, depending on context.

In Spain, the present perfect (ha comenzado) is often used for past events that are connected to the present, especially within a time period that is still considered current, such as today.

But comenzó is also perfectly natural, especially when simply narrating a past event as a finished fact.

Very roughly:

• comenzó tarde = presents it as a completed past event
• ha comenzado tarde = often feels more connected to the present moment or current situation

So the sentence as given is completely correct; it is just using the preterite viewpoint.

You would make the article, noun, and verb plural:

• Las reuniones comenzaron tarde.

Changes:

• la → las
• reunión → reuniones
• comenzó → comenzaron

But tarde stays the same, because as an adverb it does not change for number or gender.