Tu aurais pu lire la définition avant de choisir ce synonyme.

Aurais pu is the conditional perfect. It often means could have or should have been able to, and here it gives the sentence a tone of mild criticism or hindsight.

So:

• Tu avais pu lire... = you had been able to read...
• Tu aurais pu lire... = you could have read... / you might have read...

In this sentence, the speaker is basically saying that reading the definition was an available option, and implying that it would have been the better choice.

It has three parts:

• tu = you
• aurais = conditional of avoir
• pu = past participle of pouvoir
• lire = infinitive

So the pattern is:

subject + conditional of avoir + past participle of pouvoir + infinitive

This is a very common structure in French for could have + past action:

• Tu aurais pu venir. = You could have come.
• Il aurait pu appeler. = He could have called.

Because after pouvoir, French normally uses an infinitive.

So:

• pouvoir lire = to be able to read
• aurais pu lire = could have read

You do not say aurais pu lu.

This is similar to English:

• could read
• could have read

After modal verbs like can / could, English also keeps the main verb in its basic form.

Avant de + infinitive means before doing something.

So:

• avant de choisir = before choosing

French uses avant de + infinitive when the subject is the same for both actions. Here, the same person would do both actions:

• read the definition
• choose the synonym

If the subject changes, French usually uses avant que + subjunctive instead:

• Lis la définition avant qu’il choisisse le synonyme.
• Read the definition before he chooses the synonym.

But here the subject is still tu, so avant de choisir is correct.

Because synonyme begins with the consonant sound s.

French uses:

• ce before most masculine singular nouns
• cet before masculine singular nouns starting with a vowel sound or silent h

Examples:

• ce livre
• ce synonyme
• cet ami
• cet homme

So synonyme takes ce, not cet.

La définition means the definition, so it refers to a specific definition that is relevant in the context.

That suggests something like:

• there was a particular dictionary definition available
• the listener should have checked that specific definition before picking the synonym

If you said une définition, it would sound less specific:

• Tu aurais pu lire une définition...
• You could have read a definition...

That is grammatically possible, but it changes the meaning slightly.

It sounds like a mild reproach, criticism, or correction.

The speaker is not just stating a possibility. They are implying:

• you made a questionable choice
• you should probably have checked first

So the tone is close to:

• You could have read the definition before choosing that synonym.
• You might have wanted to read the definition first.

It is not extremely harsh, but it is clearly critical.

French keeps the auxiliary and the modal together before the main infinitive:

• tu aurais pu lire
• il aurait dû partir
• nous aurions voulu savoir

The order is:

subject + auxiliary in the conditional + past participle of modal verb + main infinitive

So here:

• aurais = auxiliary in the conditional
• pu = past participle of pouvoir
• lire = infinitive main verb

That is the normal order.

Yes, it could be vous if you are speaking formally or to more than one person.

The original sentence uses tu, which is:

• informal singular
• used with friends, family, children, classmates, etc.

Formal or plural version:

• Vous auriez pu lire la définition avant de choisir ce synonyme.

The grammar stays the same, except:

• tu aurais becomes vous auriez

Yes, it is natural and grammatically correct.

• choisir = to choose
• ce synonyme = this synonym

In context, it probably means the person selected a word thinking it was a good equivalent, but the speaker thinks it was the wrong choice.

French could also use other verbs depending on context, such as:

• employer ce synonyme = use this synonym
• prendre ce synonyme = take this synonym

But choisir is perfectly normal here.

Yes, in context that is often a very natural English translation.

Literally, tu aurais pu lire is you could have read. But in real usage, French conditional perfect with pouvoir often implies:

• it was possible
• it would have been wiser
• you did not do it

So depending on tone and context, English may use:

• You could have read the definition...
• You should have read the definition...

The French wording itself is a little softer and less direct than a straight Tu aurais dû lire..., which would mean You should have read... more explicitly.

A stronger, more direct criticism would be:

Tu aurais dû lire la définition avant de choisir ce synonyme.

That means:

• You should have read the definition before choosing this synonym.

Compare the two:

• Tu aurais pu lire... = You could have read... / You might have read...
• Tu aurais dû lire... = You should have read...

So pouvoir suggests an option that was available, while devoir expresses obligation or stronger judgment.

Grammatically, avant de choisir is literally before choosing.

In natural English, though, it can often be translated either as:

• before choosing
• before you chose

The French infinitive does not directly mark person, but the subject is understood from the main clause. Since the main subject is tu, the meaning is:

• before you chose this synonym

So both English versions can fit, depending on how natural you want the translation to sound.