اعتن بنفسك.

Yes. اعتن is an imperative verb, so the whole sentence is a command or strong piece of advice: Take care of yourself.

In this exact form, it is addressed to one male. In learner materials, the masculine singular is also often shown as the basic form.

The dictionary form is اعتنى بـ, which means to take care of / care for / attend to.

A few useful related forms are:

• اعتنى = he took care of
• يعتني = he takes care of / he is taking care of
• اعتنِ = take care! (to one male)

This verb is commonly followed by بـ.

It is a Form VIII verb: اعتنى.

If you like roots and patterns, its root is usually given as ع ن ي. Form VIII often adds a sense of involvement, concern, or directed attention, which fits the meaning here.

Because the imperative already includes the subject you.

So اعتن بنفسك already means you, take care of yourself. Arabic usually does not need a separate subject pronoun here unless you want extra emphasis or contrast.

That ا is part of what is called hamzat al-waṣl. It helps you begin the word with a pronounceable vowel.

At the beginning of a sentence, you pronounce it as i:

• اِعتنِ

After a preceding word, that helping vowel normally drops in connected speech.

Because this is a defective/weak verb ending in ي/ى.

In the masculine singular imperative, the final weak letter drops:

• يعتني → اعتنِ

So the written ي disappears, but in fully vowelled text you still see the final kasra:

• اِعْتَنِ

That final -i is short.

With full vowels, it is:

• اِعْتَنِ بِنَفْسِكَ

A rough pronunciation guide is:

• iʿ-ta-ni bi-naf-si-ka

A few notes:

• ع has no exact English equivalent.
• The -i at the end of اعتنِ is a short vowel.
• That helps distinguish it from the feminine command اعتني, which ends in a long ī sound.

It breaks down like this:

• بـ = with / by
• نفس = self
• -ك = your (masculine singular)

So بنفسك literally means with yourself.

But in this sentence, the whole expression is understood idiomatically as yourself in the sense of take care of yourself.

Because اعتنى normally takes the preposition بـ in Standard Arabic.

So you say:

• اعتنى بنفسه = he took care of himself
• اعتن بنفسك = take care of yourself

So اعتن نفسك would not be the normal MSA structure.

No, not in this sentence.

بنفسك can mean different things in different contexts, such as:

• yourself
• in person
• by yourself / alone

Here, because it follows اعتن بـ, it means the person receiving the care: yourself.

Because بـ is a preposition, and prepositions in Arabic make the following noun genitive.

So the fully vowelled form is:

• بِنَفْسِكَ

The important part to notice is the kasra on نفس after بـ.

Common forms are:

• to one man: اعتنِ بنفسك
• to one woman: اعتني بنفسكِ
• to a group (masculine or mixed): اعتنوا بأنفسكم

Notice two things:

• the verb changes
• with the plural, Arabic commonly uses أنفسكم for yourselves

Yes, if the context is clear, اعتنِ can work on its own as Take care.

But اعتن بنفسك is fuller and more explicit. It is especially natural when you want to say Take care of yourself clearly and warmly.

Yes. It is a natural and correct MSA expression.

It works well in formal or neutral Arabic, especially in writing, advice, or polite leave-taking. In everyday spoken Arabic, dialects often use other expressions, but اعتن بنفسك is perfectly good Modern Standard Arabic.