هيدهن المرهم النهارده.

هيدهن comes from the verb دهن, which means to apply, spread, grease, oil, or paint, depending on context.

In this sentence, because the object is المرهم (the ointment), the natural meaning is:

he will apply / spread the ointment

So this is not about painting here; it is specifically putting ointment on something.

In Egyptian Arabic, بـ usually marks the present or habitual:

• بيدهن = he applies / he is applying

The prefix هـ here marks the future:

• هيدهن = he will apply

So the sentence is future because of that initial هـ.

A useful comparison:

• بيدهن المرهم النهارده = he is applying the ointment today
• هيدهن المرهم النهارده = he will apply the ointment today

It is built into the verb.

In Arabic, verbs usually already show the subject, so you do not need a separate word for he.
The form يدهن is the he form of the verb, and with the future marker it becomes هيدهن.

So:

• هيدهن = he will apply

If you added هو before it, that would usually be for emphasis:

• هو هيدهن المرهم النهارده = he is the one who will apply the ointment today

A good approximate pronunciation is:

hayidhan el-marham en-naharda

A few notes:

• هيدهن is often pronounced something like ha-yidhan or hayidhan
• المرهم is roughly el-marham
• النهارده is roughly en-naharda

Exact vowels can vary a bit from speaker to speaker, but that pronunciation will be understood.

Because it means the ointment, not just ointment or an ointment.

• مرهم = ointment / an ointment
• المرهم = the ointment

So the sentence is referring to a specific ointment.

النهارده means today.

Yes, it is a very Egyptian Arabic word. In Modern Standard Arabic, you would more often say اليوم for today.

So this sentence sounds clearly colloquial/Egyptian, not formal MSA.

Because ن is a sun letter.

With the Arabic definite article الـ, sun letters cause the l sound to assimilate to the next consonant. So:

• النهارده is pronounced en-naharda
• not el-naharda

By contrast, م in المرهم is a moon letter, so the l is kept:

• المرهم = el-marham

This is a very common pronunciation rule in Arabic.

Because that is a very normal Arabic sentence pattern.

This sentence is:

• هيدهن = verb
• المرهم = object
• النهارده = time expression

So literally it is structured like:

will-apply the-ointment today

That is completely natural in Egyptian Arabic.

Yes. Arabic word order is flexible.

You can say:

• هيدهن المرهم النهارده
• النهارده هيدهن المرهم

Both are natural. The second version gives a little more focus to today.

The original sentence is a neutral, straightforward way to say it.

You would say:

هتدهن المرهم النهارده

So the verb changes:

• هيدهن = he will apply
• هتدهن = she will apply

A few other useful forms:

• هدهن المرهم النهارده = I will apply the ointment today
• هندهن المرهم النهارده = we will apply the ointment today
• هيدهنوا المرهم النهارده = they will apply the ointment today

In Egyptian Arabic, the easiest natural negative is:

مش هيدهن المرهم النهارده

That means:

He will not apply the ointment today.

So you can think of مش here as negating the future statement.

Yes, sometimes you can, but the nuance changes a little.

• يدهن المرهم suggests spreading/rubbing the ointment on
• يحط المرهم is more general: put the ointment on

So with ointment, يدهن is a very good and natural choice because it emphasizes the act of applying it onto a surface or body part.