Hyresvärden måste återbetala depositionen.

Because hyresvärd is an en-word (common gender noun), and -en is the usual definite singular ending.

• en hyresvärd = a landlord
• hyresvärden = the landlord

So hyresvärden means a specific landlord, not just any landlord.

For the same reason: deposition is also an en-word, so its definite singular form is depositionen.

• en deposition = a deposit
• depositionen = the deposit

In this sentence, it refers to a specific deposit already known from the context, so Swedish uses the definite form.

Swedish often uses the definite form when both speaker and listener know which person or thing is meant.

Here, the sentence is talking about:

• the landlord involved in the situation
• the deposit connected to that rental

So definite forms are natural. English does this with the separate word the, while Swedish often puts definiteness at the end of the noun.

Måste means must or has to.

It is the present-tense form of the verb måste / historically connected to må in older grammar discussions, but for learners it is best to simply learn måste as the modal verb meaning must / have to.

Examples:

• Jag måste gå. = I must go.
• Hyresvärden måste återbetala depositionen. = The landlord must refund the deposit.

A useful thing to remember: after måste, the next verb stays in the infinitive.

Because after modal verbs in Swedish, you normally use the bare infinitive, just like in English.

• must pay
• måste betala

So:

• måste återbetala = must repay / must refund

You do not say måste att återbetala.

Återbetala is made up of:

• åter- = back, again
• betala = pay

So it literally means pay back, and in natural English it is often repay or refund.

That makes this sentence very transparent once you know the parts:

• återbetala depositionen = pay back the deposit / refund the deposit

Yes, very often you can. Both are understandable:

• återbetala depositionen
• betala tillbaka depositionen

They are close in meaning. Återbetala is a bit more compact and often feels slightly more formal or official, while betala tillbaka is very common in everyday speech.

In Swedish, verbs do not change according to the person or number of the subject.

So you get:

• jag måste
• du måste
• han måste
• vi måste

The verb form stays the same. This is much simpler than English in many cases.

The basic order here is:

Subject + finite verb + infinitive + object

• Hyresvärden = subject
• måste = finite verb
• återbetala = infinitive
• depositionen = object

So the sentence follows a very normal Swedish main-clause pattern.

Yes. It is made from:

• hyra / hyres- = rent, rental
• värd = host, keeper, proprietor

So hyresvärd is literally something like rental host, but the real meaning is landlord.

Swedish uses compound words very often, and learning to spot the parts can help a lot.

A rough guide for an English speaker:

• återbetala ≈ AW-ter-beh-TAH-la
• hyresvärden ≈ HEW-res-vehr-den

A few useful pronunciation notes:

• å sounds roughly like the vowel in British law
• ä sounds somewhat like the vowel in bed, though not exactly
• hy has a rounded vowel that English does not really have, so it may take practice

The stress is usually:

• Å-ter-be-TA-la
• HY-res-vär-den

They are:

• en hyresvärd = a landlord
• en deposition = a deposit

And the definite forms are:

• hyresvärden = the landlord
• depositionen = the deposit

So a useful pattern is:

• en + noun = indefinite
• noun + -en = definite, for many common gender nouns

Yes. In many contexts, måste can be translated as either:

• must
• has to
• sometimes even needs to, depending on tone

So Hyresvärden måste återbetala depositionen can naturally mean:

• The landlord must refund the deposit
• The landlord has to refund the deposit

The exact English wording depends on context and style.