Ngăn bí mật ở trong bàn.

In Vietnamese, descriptive words usually come after the noun, not before it.

So:

• ngăn bí mật = secret compartment
• literally: compartment secret

This is very normal Vietnamese word order. English says secret compartment, but Vietnamese says compartment secret.

Here, ngăn means a compartment, section, or sometimes a drawer-like space.

It is a general word for a divided space inside something. Depending on context, it could refer to:

• a compartment in a desk
• a section in a cabinet
• a hidden storage space

If you specifically mean a pull-out drawer, Vietnamese often uses ngăn kéo. But ngăn by itself is broader and works well for compartment.

Ở trong means in / inside.

It is made of:

• ở = at, in, located at
• trong = inside

Together, ở trong emphasizes location inside something.

So ở trong bàn means inside the desk/table.

In many cases, you could also just say trong bàn. Adding ở makes the location function more explicit.

Vietnamese does not always use a separate verb like English is.

In location sentences, ở often does the job of expressing where something is located.

So:

• Ngăn bí mật ở trong bàn.
• literally something like: Secret compartment located inside desk.

This corresponds to English The secret compartment is in the desk.

So the sentence does have the idea of is, but it is expressed through the location structure, especially ở.

Bàn can mean either table or desk, depending on context.

Examples:

• bàn ăn = dining table
• bàn học = desk / study table
• bàn làm việc = work desk

In your sentence, if the English meaning shown is something like The secret compartment is in the desk, then bàn is being understood as desk from context.

Without extra context, bàn by itself can be ambiguous.

Yes, trong bàn would also be correct in many situations.

Compare:

• Ngăn bí mật ở trong bàn.
• Ngăn bí mật trong bàn.

Both can mean the same thing here.

A rough difference:

• trong = simply in/inside
• ở trong = a little more explicitly located inside

In everyday speech, both are natural. Vietnamese often allows both patterns.

Yes, it can be a complete sentence, especially if you are talking about a specific compartment already known from context.

It sounds like:

• The secret compartment is inside the desk.

However, if you are introducing it for the first time, Vietnamese often prefers:

• Có một ngăn bí mật ở trong bàn.
• There is a secret compartment in the desk.

So the version without có một feels more like you are referring to the secret compartment, not just saying one exists.

Vietnamese usually does not use articles the way English does.

English distinguishes:

• a secret compartment
• the secret compartment

Vietnamese often leaves that unstated, and the listener figures it out from context.

So ngăn bí mật could mean:

• a secret compartment
• the secret compartment

depending on the situation.

If you want to make a clearer, you can say:

• một ngăn bí mật = a secret compartment

If you want to make something more definite, context usually does the work.

Yes, bí mật can be a noun in other contexts, meaning secret.

For example:

• giữ bí mật = keep a secret
• một bí mật = a secret

But in ngăn bí mật, it is functioning as a description of ngăn, so it means secret/hidden.

Vietnamese words often have flexible word-class behavior, and their role is understood from position and context.

Usually both ideas are close, and either may work in translation.

• secret compartment is the most direct translation
• hidden compartment is often a very natural English rendering

Vietnamese bí mật literally relates to secret, but in context it can imply something concealed or not meant to be noticed. So English may translate it in the way that sounds most natural in context.

A few things may be tricky for English speakers:

• ngăn: the ng sound occurs at the beginning of the word. English has this sound in sing, but not usually at the start of a word.
• bí mật: both syllables have tones, and the final t in mật is unreleased and short.
• ở: has the ở vowel, which does not match a simple English vowel.
• bàn: has a falling tone.

It helps to practice syllable by syllable:

• Ngăn
• bí mật
• ở trong
• bàn

Then say the whole sentence smoothly.

Yes, but changing the word order changes the focus.

Original:

• Ngăn bí mật ở trong bàn.
• Focus: The secret compartment is in the desk.

Another common pattern:

• Trong bàn có một ngăn bí mật.
• literally: In the desk there is a secret compartment.
• Focus: the existence of the compartment

So Vietnamese can express the same basic idea in different ways depending on what you want to emphasize:

• the thing itself
• the location
• the existence of it