Giáo viên rất nghiêm.

Giáo viên means teacher.

A few useful notes:

• It is a general word for teacher.
• It does not show gender, so it can mean a male or female teacher.
• It can also be understood as teachers in the right context, because Vietnamese nouns usually do not change form for singular vs. plural.

So giáo viên could mean:

• the teacher
• a teacher
• teachers

The exact meaning depends on context.

In Vietnamese, you often do not need a verb like to be before an adjective.

So:

• Giáo viên rất nghiêm. = The teacher is very strict.

Literally, the structure is more like:

• teacher + very + strict

This is completely normal in Vietnamese.
When describing someone or something with an adjective, Vietnamese usually does not use a separate word for is.

Rất means very.

It goes before the adjective it modifies:

• rất nghiêm = very strict

So the sentence structure is:

• Giáo viên = teacher
• rất = very
• nghiêm = strict / stern / serious

This placement is normal in Vietnamese:

• Anh ấy rất cao. = He is very tall.
• Cô ấy rất tốt. = She is very kind/good.

It can, but there is a nuance.

Nghiêm often means:

• serious
• stern
• strict in some contexts

When talking about a person’s personality or behavior, Vietnamese often uses nghiêm khắc for strict more explicitly.

So:

• Giáo viên rất nghiêm. = The teacher is very stern/serious/strict.
• Giáo viên rất nghiêm khắc. = The teacher is very strict.

Your sentence is grammatical, but in many situations nghiêm khắc may sound more natural if you specifically want strict.

Yes, it can, depending on context.

Because Vietnamese often leaves out:

• articles like a and the
• plural marking like -s

So giáo viên could be understood as:

• the teacher
• a teacher
• teachers

Context decides the most natural meaning.

If you want to make it clearer, you could say:

• Người giáo viên đó rất nghiêm. = That teacher is very strict/stern.
• Các giáo viên rất nghiêm. = The teachers are very strict/stern.

Yes, it is grammatical and understandable.

However, in real conversation, speakers often make it more specific. For example:

• Cô giáo rất nghiêm. = The female teacher is very strict/stern.
• Thầy giáo rất nghiêm. = The male teacher is very strict/stern.
• Giáo viên này rất nghiêm. = This teacher is very strict/stern.
• Giáo viên rất nghiêm khắc. = The teacher is very strict.

So your sentence is fine, but in everyday speech people often add more detail.

Vietnamese does not use articles the same way English does.

English requires choices like:

• a teacher
• the teacher

Vietnamese usually just says:

• giáo viên

Then the listener understands the exact meaning from context.

If needed, Vietnamese can add words to make the meaning clearer:

• một giáo viên = a teacher
• giáo viên đó = that teacher / the teacher
• giáo viên này = this teacher

But in many simple sentences, just giáo viên is enough.

A simple approximate pronunciation is:

• giáo viên → roughly zow vee-en in Northern Vietnamese
• rất → roughly zut
• nghiêm → roughly ngee-uhm

A few important pronunciation points:

• giáo has a rising tone.
• viên is fairly level.
• rất has a sharp tone and a short vowel.
• nghiêm begins with the ng sound, like the end of sing.

Regional pronunciation differs, especially for gi and r, so what you hear may vary between North and South.

The pattern is:

Subject + degree word + adjective

So here:

• Giáo viên = subject
• rất = degree word
• nghiêm = adjective

This pattern is very common in Vietnamese:

• Trời rất nóng. = The weather is very hot.
• Căn phòng rất nhỏ. = The room is very small.
• Cô ấy rất đẹp. = She is very beautiful.

So Giáo viên rất nghiêm. follows a very common and useful sentence pattern.