Μην πας στα βαθιά χωρίς σωσίβιο.

Μην is used to make a negative command or warning.

So:

• Μην πας = Don’t go

This is different from δεν, which is used for ordinary negation in statements:

• Δεν πας = You are not going
• Μην πας = Don’t go

So here Μην shows that the speaker is telling someone not to do something.

Yes, πας can look like the ordinary you go form, but after μην it is understood as part of a command structure.

In this sentence, μην πας means don’t go.

It is best to think of it as the form Greek uses for a single, whole action:

• Μην πας = don’t go / don’t head there

A useful contrast is:

• Μην πας = don’t go there once, don’t set off, don’t enter
• Μην πηγαίνεις = don’t keep going, don’t go regularly, don’t be going

So Μην πας is the more natural choice for a warning about one act.

It is speaking to one person, informally.

That is because πας is the 2nd person singular form.

If you wanted to say the same thing to more than one person, or to one person formally, you would say:

• Μην πάτε στα βαθιά χωρίς σωσίβιο.

So:

• πας = you, singular, informal
• πάτε = you, plural or formal

Στα is simply the contracted form of:

• σε + τα = στα

This is extremely common in Greek.

So:

• στα βαθιά literally means something like to/in the deep parts

Also, in Modern Greek, σε can be used both for location and for movement toward a place. So with πας, στα βαθιά can mean:

• into the deep water
• to the deep end

Στα βαθιά is a very common expression meaning into deep water or into the deep end.

Literally, βαθιά is the neuter plural form of deep, but here it is being used almost like a noun.

So Greek is really saying something like:

• into the deep [waters/parts]

In everyday speech, Greek often leaves out the noun when it is obvious from context.

Yes, you can think of one as being understood.

A fuller version could be:

• στα βαθιά νερά = into the deep waters

But in natural Greek, στα βαθιά is perfectly normal on its own, especially in contexts like swimming, the sea, or a pool.

So the sentence does not sound incomplete to a Greek speaker.

Because χωρίς σωσίβιο means without a life jacket / without any life jacket in a general, indefinite sense.

Greek often leaves out the article after χωρίς when the meaning is general:

• χωρίς σωσίβιο = without a life jacket
• χωρίς το σωσίβιο = without the life jacket, without that specific life jacket

So the version in your sentence is the natural one if the speaker means don’t go in without wearing one.

The dictionary form is:

• το σωσίβιο

It is a neuter singular noun.

In this sentence, it appears as σωσίβιο, which for many neuter nouns looks the same in both the nominative and accusative.

Useful forms:

• singular: το σωσίβιο
• plural: τα σωσίβια

After χωρίς, Greek uses the accusative form, but with this noun the form does not change.

Yes. Μη πας is also used and means the same thing.

Both μη and μην are heard in Modern Greek. In a sentence like this, μην is very common and very standard, so Μην πας is an excellent form to learn.

So:

• Μην πας στα βαθιά...
• Μη πας στα βαθιά...

Both are acceptable.

It can be both.

Literally, it means going into deep water.

Figuratively, στα βαθιά can also mean something like:

• into the deep end
• into a difficult situation without preparation

So Greek can use this expression the way English says someone was thrown in at the deep end.

In your sentence, because of χωρίς σωσίβιο, the meaning sounds strongly literal, but the phrase itself can definitely be used metaphorically too.