صديقي نسي مفتاحه بالبيت.

Word by word:

• صديقي = my friend
• نسي = forgot
• مفتاحه = his key
• بالبيت = at home / in the house

So the full sentence means: My friend forgot his key at home / in the house.

Because the ending -ي means my.

• صديق = friend
• صديقي = my friend

This is a very common way to show possession in Arabic: you attach a pronoun suffix directly to the noun instead of using a separate word like my.

In Arabic, possessive pronouns are often attached directly to the noun.

• مفتاح = key
• مفتاحه = his key

The ending -ه means his.

So instead of saying two separate words like in English, Arabic combines them into one word.

Not always 100% by grammar alone. مفتاحه literally means his key, but his could refer to a male already understood from context.

In this sentence, the most natural reading is that his refers to my friend, so: My friend forgot his key.

But in a different context, it could theoretically refer to another male person. Context usually makes this clear.

Because Arabic often leaves out subject pronouns when the verb already shows the subject.

Here, نسي already means he forgot in context. So you do not need to add a separate word for he.

This is very normal in Arabic. English usually needs he, but Arabic often does not.

This sentence starts with the subject:

• صديقي = subject
• نسي = verb
• مفتاحه = object
• بالبيت = place

So the order here is basically:

Subject + Verb + Object + Place

That is very natural in Levantine Arabic.

Arabic can also use verb-first order in some situations, but this sentence is completely normal as it is.

بالبيت is made of:

• بـ = in / at
• البيت = the house

Together:

• بالبيت = in the house or at home

The بـ attaches to the following word, so it is written as one unit.

Also, because بـ comes before ال, the pronunciation becomes smooth: bil-bēt.

It can mean either, depending on context.

In Levantine, بالبيت often means at home, not just physically inside the house. So in this sentence, a very natural English translation is:

My friend forgot his key at home.

But literally it is still in the house.

It is usually pronounced something like nisi or nese depending on the speaker and region.

A simple learner-friendly pronunciation is:

nisi

The important thing is that it is the past tense verb forgot.

Yes. صديقي normally means my male friend.

Also, مفتاحه contains -ه, which means his.

If you wanted to talk about a female friend, you would change the sentence. For example, in Levantine you might say something like:

صديقتي نسيت مفتاحها بالبيت = My female friend forgot her key at home

So the original sentence is masculine.

It sounds natural in Levantine Arabic.

A few clues:

• بالبيت is very common in spoken Levantine.
• The whole sentence has an everyday spoken feel.

In Modern Standard Arabic, you could also say something very similar, but the style would usually be more formal. For example:

صديقي نسي مفتاحه في البيت

That said, the original sentence is perfectly understandable and very natural in Levantine speech.

There actually is the inside بالبيت.

• بيت = house
• البيت = the house
• بالبيت = in the house / at home

So Arabic is not missing the here. It is just built into the word.

Yes, in many situations you can.

• بالبيت = at home / in the house
• في البيت = in the house

In Levantine, بالبيت is extremely common for at home.
في البيت is also correct, but can sometimes sound a bit more literal or slightly more formal depending on context.

So for everyday Levantine, بالبيت is a very natural choice.