À huit heures, la sonnerie retentit.

Because à and a are two different words in French.

• à = a preposition, usually meaning at, to, or in
• a = the verb has from avoir

So in À huit heures, the accent is required because this à means at.

They are used for different things:

• À huit heures = At eight o’clock
  This gives the time when something happens.
• Il est huit heures = It is eight o’clock
  This tells you what time it is right now.

So in À huit heures, la sonnerie retentit, the first part is just setting the time for the action.

French uses heure in the singular only with one o’clock:

• une heure
• deux heures
• trois heures
• huit heures

So huit heures is plural because it is more than one hour.

French often puts a time expression at the beginning of the sentence to set the scene or frame the action.

So:

• À huit heures, la sonnerie retentit.
• La sonnerie retentit à huit heures.

Both are correct.

The comma is there because À huit heures is an introductory phrase. In English, we do the same kind of thing in sentences like At eight o’clock, the bell rings.

La sonnerie usually means the bell signal, ringing, or buzzer sound, not necessarily the physical bell itself.

Depending on the situation, it could mean:

• a school bell
• a door buzzer
• a phone ring tone
• the sound made by a bell system

So it is often closer to the ringing/the bell signal than to the object bell itself.

La is the definite article, so it refers to a specific bell signal that is already known in the situation.

For example, in a school, la sonnerie would naturally mean the bell everyone is expecting.

If you said une sonnerie, it would sound more like a ringing sound or some bell sound, not a specific familiar one.

Retentit comes from retentir, which means to ring out, to resound, or to echo out.

It is a bit stronger and more vivid than sonne.

• sonner = to ring
• retentir = to ring out / resound

So la sonnerie retentit sounds a little more dramatic or literary than a simpler sentence like la cloche sonne.

By itself, retentit can be ambiguous.

It can be:

• present tense: it rings / it rings out
• passé simple: it rang out

The form is the same in both cases.

So the tense is decided by context. In a standalone sentence like this, it is often understood as present time or as a general statement. But in a literary story written in the past, it could mean rang out.

A few important points:

• heures begins with a silent h
• the final t in huit is pronounced here because the next word begins with a vowel sound
• the whole group flows together smoothly: huit heures

A rough pronunciation is:

• À huit heures ≈ ah weet-uhr

That said, the French ui sound in huit is not exactly like English wee, so that is only an approximation.

Normally, à huit heures means at eight o’clock, so it suggests a specific time.

If you want to say around eight, French would usually say:

• vers huit heures = around eight
• aux alentours de huit heures = around eight / roughly around eight

So à huit heures is the more exact expression.