Amanhã o veterinário vai vacinar o cachorro.

Amanhã means tomorrow. In Portuguese, time expressions often go at the beginning of the sentence, especially when setting the scene.

So:

Amanhã o veterinário vai vacinar o cachorro.
= Tomorrow the veterinarian is going to vaccinate the dog.

You could also say:

O veterinário vai vacinar o cachorro amanhã.

That is also correct. Putting amanhã first just gives it a little more emphasis.

O means the. Portuguese uses definite articles much more often than English does.

So o veterinário literally means the veterinarian.

In English, you might say The vet will vaccinate the dog or sometimes just Vet will vaccinate the dog is impossible; English usually needs the too here. But in Portuguese, articles are also commonly used before professions and nouns in contexts where English may be less strict.

If the veterinarian were female, it would be:

A veterinária

Because o cachorro means the dog.

Portuguese usually keeps the article when talking about a specific noun like this. So:

• o cachorro = the dog
• um cachorro = a dog

If you changed the sentence to um cachorro, it would mean the vet is vaccinating a dog, not a specific dog.

Vai vacinar is a very common way to express the future in Brazilian Portuguese.

It is made with:

• vai = goes / is going
• vacinar = to vaccinate

Together, vai vacinar means is going to vaccinate / will vaccinate.

Portuguese also has a simple future form:

vacinará

So you could say:

Amanhã o veterinário vacinará o cachorro.

This is correct, but in everyday Brazilian Portuguese, vai vacinar sounds more natural and conversational.

Because after forms of ir used for the near future, the next verb stays in the infinitive.

Pattern:

ir + infinitive

Examples:

• vou estudar = I am going to study
• vamos sair = we are going to leave
• vai vacinar = he/she is going to vaccinate

So vai vacinar is built exactly the way Portuguese normally forms this kind of future.

Vai is the ele/ela/você form of the verb ir, which means to go.

Conjugation:

• eu vou
• você/ele/ela vai
• nós vamos
• eles/elas/vocês vão

In this sentence, the subject is o veterinário, which is third-person singular, so the correct form is vai.

The subject is o veterinário, because it comes before the verb phrase vai vacinar.

So the structure is:

• Amanhã = time expression
• o veterinário = subject
• vai vacinar = verb phrase
• o cachorro = object

That means the veterinarian is doing the vaccinating, and the dog is receiving the action.

Yes, to some extent.

These are all possible:

• Amanhã o veterinário vai vacinar o cachorro.
• O veterinário vai vacinar o cachorro amanhã.

Both are natural.

You can also sometimes move parts around for emphasis, but the most neutral word order is usually subject + verb + object, with time expressions either at the beginning or end.

Both can mean dog, but cachorro is much more common in everyday Brazilian Portuguese.

• cachorro = the usual everyday word for dog
• cão = more formal, more literary, and also used in certain fixed expressions

So in normal speech, o cachorro sounds very natural.

Yes, they matter.

Accent marks in Portuguese are part of the correct spelling and often show stress or pronunciation.

• amanhã has ã, which shows a nasal sound
• veterinário has á, which shows the stressed syllable

If you leave accents out, people may still understand you in casual typing, but it is not correct spelling and can sometimes cause confusion.

A rough English-friendly guide is:

ah-ma-NYÃ

Important points:

• the last syllable is stressed
• nh sounds like the ny in canyon
• ã is nasal, so the sound comes partly through the nose

So it does not sound like a plain final a.

A rough guide is:

veh-teh-ree-NAH-ryoo

The stress falls on ná because of the accent mark:

ve-te-ri-NÁ-rio

In Brazilian Portuguese, the final rio here is usually said smoothly, not like the English word Rio by itself.

In this sentence, yes: o veterinário is masculine singular.

If the veterinarian is female, you would say:

Amanhã a veterinária vai vacinar o cachorro.

So the article and noun change together:

• o veterinário = the male veterinarian
• a veterinária = the female veterinarian

Yes. In natural English, vai vacinar can be translated as either:

• is going to vaccinate
• will vaccinate

The Portuguese structure is clear future meaning, but English has more than one natural way to express that same idea.

No, not in standard Portuguese.

Portuguese normally needs the articles here:

• o veterinário
• o cachorro

Without them, the sentence sounds ungrammatical or very unnatural in this context.

So the full sentence should stay:

Amanhã o veterinário vai vacinar o cachorro.