דלת הסתרים סגורה במנעול תלייה.

In Hebrew, the verb to be is usually omitted in the present tense.

So:

• דלת הסתרים סגורה = The secret door is closed
• literally, Hebrew just says something like The secret door closed

This is very normal in Hebrew nominal sentences.

If you wanted past or future, Hebrew would use a form of היה:

• דלת הסתרים הייתה סגורה = The secret door was closed
• דלת הסתרים תהיה סגורה = The secret door will be closed

Because this is a construct chain (in Hebrew: סמיכות).

In a construct chain:

• the first noun is in a linked form
• the definiteness is usually shown on the second noun

So:

• דלת הסתרים literally looks like door of the secrets/hidden things
• but as a phrase it means the secret door

This is why Hebrew does not say הדלת הסתרים here.

A similar pattern is:

• בית הספר = the school
  literally: house of the book

So דלת הסתרים is following a very common Hebrew pattern.

Yes. הדלת הסודית is also a perfectly natural way to say the secret door.

The difference is mostly stylistic:

• הדלת הסודית = adjective structure, very straightforward: the secret door
• דלת הסתרים = construct-chain style, often feels a bit more literary, set-phrase-like, or dramatic

So both can work, but דלת הסתרים has a slightly more special or story-like feel.

Because דלת is a feminine singular noun, and the adjective/predicate must agree with it.

So:

• דלת = feminine singular
• therefore סגורה = feminine singular

Compare:

• החלון סגור = The window is closed
  (חלון is masculine singular)
• הדלת סגורה = The door is closed
• הדלתות סגורות = The doors are closed

This kind of agreement is very important in Hebrew.

Because here סגורה is a predicate adjective, not an adjective directly attached to the noun.

Compare these two patterns:

• הדלת הסגורה = the closed door
  Here closed directly describes door, so it takes ה־ too.
• הדלת סגורה = the door is closed
  Here closed is the predicate, so it does not take ה־.

Your sentence is the second type:

• דלת הסתרים סגורה = The secret door is closed

So סגורה stays without ה־.

Here ב־ means with or by means of.

So:

• במנעול תלייה = with a padlock

Even though ב־ often means in, it has several uses in Hebrew. In this sentence it is instrumental:

• סגורה במנעול תלייה = closed/secured with a padlock

So do not translate ב־ mechanically as only in. Its meaning depends on context.

מנעול תלייה means padlock.

Literally, it is something like:

• מנעול = lock
• תלייה = hanging

So the phrase is basically a hanging lock, which is why it means padlock.

This is another noun-noun combination, similar to a construct phrase. In normal English terms, you can just learn it as one vocabulary item:

• מנעול תלייה = padlock

Also notice that it is indefinite here:

• במנעול תלייה = with a padlock
• not with the padlock

Good question. There is a nuance here.

• סגור / סגורה = closed / shut
• נעול / נעולה = locked

So סגורה במנעול תלייה suggests that the door is shut and secured with a padlock.

If you want to stress the idea of being locked, Hebrew could also say:

• דלת הסתרים נעולה במנעול תלייה = The secret door is locked with a padlock

So the given sentence is understandable and natural, but נעולה would be more explicitly locked.

The sentence breaks down like this:

• דלת הסתרים = the subject, the secret door
• סגורה = the predicate adjective, closed
• במנעול תלייה = a prepositional phrase, with a padlock

So the overall structure is:

• [subject] + [predicate adjective] + [prepositional phrase]

That gives:

• דלת הסתרים סגורה במנעול תלייה.
• The secret door is closed with a padlock.

This is a very common Hebrew sentence pattern.

It is fairly similar to English in this sentence.

Hebrew has:

• subject: דלת הסתרים
• then the predicate: סגורה
• then extra information: במנעול תלייה

So it lines up pretty neatly with:

• The secret door
  • is closed
    • with a padlock

The main difference from English is not the word order, but the fact that Hebrew omits the present-tense word is.