geugeon ajik bimirinikka somuneul naemyeon an dwaeyo.

그건 is a contraction of 그거는.

• 그거 = that thing
• 는 = topic marker

So:

• 그거는 → full form
• 그건 → shortened, very common in everyday speech

In this sentence, 그건 means as for that or simply that.

아직 means still or yet.

In this sentence, it gives the idea that the thing is not ready to be made public yet:

• 아직 비밀 = still a secret

So the speaker is saying that the matter is currently still secret.

비밀 is a noun, so to say is a secret, Korean uses the copula 이다.

• 비밀이다 = to be a secret

When you attach -(으)니까 to a noun + 이다, it becomes:

• 비밀이니까 = because it is a secret

So the 이 is part of the copula structure, not a separate subject marker.

-(으)니까 means because or since.

So:

• 비밀이니까 = because it’s a secret

This ending is very common when giving a reason, especially when that reason supports a suggestion, request, command, or warning.

That fits this sentence well:

• Because it’s still a secret, you must not spread rumors / tell people about it.

Both can mean because it’s a secret, but -(으)니까 is especially natural when the second part is a command, prohibition, suggestion, or request.

Here the second part is:

• 소문을 내면 안 돼요 = you must not spread it around

Because that is basically a prohibition, 비밀이니까 sounds very natural.

A learner-friendly way to think about it:

• -아서/어서, -이라서: often used for simple explanation of cause
• -(으)니까: often used when the speaker is giving advice, orders, warnings, or reasons for them

Yes, it functions like a set expression.

• 소문 = rumor, word, talk, gossip
• 내다 = to put out, produce, send out

Together, 소문을 내다 means:

• to spread a rumor
• to spread the word
• to let people know
• to make something known around

In this sentence, it has the sense of spreading it around or letting it get out.

Because the previous clause says it is still a secret, the meaning is basically:

• Don’t let the news get around
• Don’t spread rumors about it
• Don’t tell people about it

을 is the object marker.

In 소문을 내다, the thing being put out / spread is 소문, so it takes the object marker:

• 소문을 내다

This is the standard dictionary-style expression.

Yes, you may sometimes see 소문내다 written as one word in real usage.

However, the more standard spacing is:

• 소문을 내다

So in careful writing, 소문을 내면 안 돼요 is a very normal form.

For learners, it is safest to remember it as:

• 소문을 내다 = to spread rumors / spread the word

This comes from the grammar pattern:

• -면 안 되다 = must not, should not, it is not allowed to

Breakdown:

• 내면 = if one spreads it / if one lets it out
• 안 돼요 = it won’t do / it’s not okay

Together:

• 소문을 내면 안 돼요 = You must not spread it around

Literally, it is something like:

• If you spread it, it won’t do

But in natural English, it means:

• Don’t spread it around
• You mustn’t let it get out

Yes, usually it is.

Compare these:

• 소문을 내지 마세요 = Please don’t spread it
• 소문을 내면 안 돼요 = You must not spread it / It’s not okay to spread it

Both can be used to tell someone not to do something, but -면 안 돼요 often sounds like explaining a rule, limit, or situation rather than giving a blunt direct command.

So this sentence feels like:

• Because it’s still secret, you’re not supposed to spread it around.

That can sound a little more explanatory and less abrupt.

No, the subject is not stated explicitly.

Korean often leaves out subjects when they are understood from context. In this kind of sentence, the implied subject is usually:

• you
• or people in general

So 소문을 내면 안 돼요 usually means:

• You shouldn’t spread it around
• or It shouldn’t be spread around

The exact interpretation depends on context.

The sentence is:

• 그건 아직 비밀이니까 소문을 내면 안 돼요.

It breaks down like this:

1. 그건 = as for that
2. 아직 비밀이니까 = because it is still a secret
3. 소문을 내면 안 돼요 = you must not spread it around

So the structure is:

• Reason + result/prohibition

This is very common in Korean: the reason comes first, and the main statement comes after.

Not always completely bad, but it often has the feeling of word spreading around, gossip, or rumor, rather than a neutral official announcement.

That is why this sentence can sound a little like:

• Don’t go around telling people
• Don’t let it become gossip
• Don’t spread it around

If the speaker only wanted to say don’t tell anyone, other expressions might also be used depending on context. But 소문을 내다 strongly emphasizes making it known around to others.

돼요 is the polite present form of 되다.

In 안 되다, it means:

• to not be allowed
• to not be okay
• to not work / not do

So:

• 안 돼요 = it’s not okay / you must not

This makes the sentence polite, but still natural and common in everyday speech.

If you changed the politeness level:

• 안 돼 = casual
• 안 됩니다 = more formal
• 안 돼요 = polite everyday style

It is very natural.

그건 아직 비밀이니까 소문을 내면 안 돼요 sounds like something someone would say when they want to stop information from spreading before the right time.

The tone is:

• polite
• explanatory
• cautioning someone not to talk about it publicly

A very natural English sense would be:

• That’s still a secret, so you mustn’t spread it around.
• That’s still confidential, so don’t let it get out.