من مطمئنم که او هم میآید، اما احتمالا دیر میرسد.

که introduces a subordinate clause, much like that in English.

So:

• من مطمئنم = I am sure
• که او هم می‌آید = that he/she is coming too

Together: I am sure that he/she is coming too.

In English, that is often optional, but in Persian که is very common in this kind of sentence after verbs and expressions like:

• می‌دانم که... = I know that...
• فکر می‌کنم که... = I think that...
• مطمئنم که... = I’m sure that...

Sometimes Persian speakers omit که in casual speech, but using it here is completely natural.

مطمئنم is a shortened spoken-and-written form of:

• مطمئن هستم

Both mean I am sure.

Here is the breakdown:

• مطمئن = sure / certain
• -م = I am / my / me, depending on context

In this sentence, -م functions as the first-person singular ending attached to the predicate, so مطمئنم means I am sure.

This kind of shortening is very common in Persian:

• خسته‌ام = I am tired
• خوشحالم = I am happy
• مطمئنم = I am sure

So yes, it is effectively a contracted form.

Yes, من can be omitted.

Persian often drops subject pronouns when the verb or ending already makes the subject clear. Since مطمئنم already shows I, you can say:

• مطمئنم که او هم می‌آید...

and it still clearly means I’m sure that...

Including من adds emphasis or contrast, for example:

• من مطمئنم... = I’m sure... / As for me, I’m sure...

So:

• من مطمئنم... = slightly more explicit or emphatic
• مطمئنم... = very natural and common

هم usually means also, too, or as well.

In this sentence:

• او هم می‌آید = he/she is coming too

It suggests someone else is coming, and he/she is included as well.

A key point is that هم usually comes right after the word it emphasizes:

• او هم می‌آید = he/she too is coming
• من هم می‌آیم = I am coming too

So here, هم is attached in meaning to او.

Yes, you could often say اون instead in everyday speech.

• او = a more formal, written, or neutral he/she
• اون = common spoken he/she/that person

So these are both possible:

• او هم می‌آید
• اون هم میاد (more colloquial spelling/speech)

A learner should know that او is very common in textbooks and formal writing, while اون is what you will hear a lot in conversation.

Also, Persian does not mark gender in pronouns, so او can mean either he or she.

می‌آید is the present tense / habitual-present form of آمدن (to come).

Breakdown:

• می- = present/imperfective marker
• آید / the stem-based ending here gives the meaning comes / is coming

In modern Persian, this form can mean:

• comes
• is coming
• sometimes will come, depending on context

In your sentence, because the meaning is already understood from context, می‌آید is best taken as is coming or will come.

Persian present forms often cover meanings that English separates into simple present and present continuous.

Examples:

• می‌آید = comes / is coming
• می‌رسد = arrives / is arriving

Yes. In standard Persian spelling, these are usually written with a half-space after می:

• می‌آید
• می‌رسد

What you saw:

• میآید
• میرسد

is understandable, and many people type this way informally, but the more standard written form uses a half-space.

So the polished version of the sentence would be:

• من مطمئنم که او هم می‌آید، اما احتمالاً دیر می‌رسد.

This is mostly an orthographic issue, not a grammar issue.

Both mean but.

• اما is a bit more formal or written
• ولی is very common in everyday speech

So these are both natural:

• ... اما احتمالاً دیر می‌رسد
• ... ولی احتمالاً دیر می‌رسد

In textbooks and written Persian, you often see اما. In casual speech, ولی may sound more natural.

احتمالا means probably.

In this sentence:

• اما احتمالا دیر می‌رسد = but probably he/she arrives late / will arrive late

It is an adverb, so it modifies the whole idea of the clause. Persian adverbs like this are fairly flexible, but they often come before the part they modify.

Natural positions include:

• اما احتمالا دیر می‌رسد
• اما دیر می‌رسد احتمالا — less common in neutral writing
• او احتمالا دیر می‌رسد — also natural

A spelling note: in formal writing, you may also see احتمالاً with the tanvin-style ending. Both احتمالا and احتمالاً are common, but احتمالاً is often considered more formal/standard.

Because دیر is an adverb meaning late, and in Persian adverbs commonly come before the verb.

So:

• دیر می‌رسد = arrives late / will arrive late

This word order is very natural in Persian.

Other examples:

• زود می‌آید = he/she comes early
• خوب صحبت می‌کند = he/she speaks well
• آرام راه می‌رود = he/she walks calmly

So دیر before the verb is exactly what you should expect.

It can mean either, depending on context.

رسیدن means to arrive / to reach, and می‌رسد is the present-form verb. In Persian, this form is often used for:

• habitual present: arrives
• ongoing present: is arriving
• near future or context-based future: will arrive

In your sentence, with احتمالا and the overall meaning, the natural English translation is often:

• but he/she will probably arrive late

So even though Persian does not use a separate future form here, the meaning can still be future.

A very common conversational version would be something like:

• مطمئنم که اونم میاد، ولی احتمالاً دیر می‌رسه.

Compared with the original:

• او becomes اون
• اما becomes ولی
• می‌آید becomes spoken میاد
• می‌رسد becomes spoken می‌رسه

This is not a different grammar structure; it is just more colloquial.

So the original sentence is perfectly correct, but a learner should know that real spoken Persian often sounds less formal than the textbook version.

Yes, مطمئن is a word many learners find awkward at first.

It is usually pronounced approximately like:

• motma'en

There is a little break between the vowels in the second part, because of the ئ. It is not a smooth single syllable like English certain. You can think of it as something like:

• mot-ma-en

And مطمئنم is approximately:

• motma'enam

You do not need to pronounce it perfectly right away, but it helps to know that the ئ often signals a slight separation or glottal break.

Yes, often it can.

Persian frequently drops subject pronouns when the meaning is clear from context. So you could say:

• من مطمئنم که هم می‌آید، اما احتمالا دیر می‌رسد

But this version may sound less natural because هم usually needs something explicit to attach to. A more natural omission would be in the second clause only:

• من مطمئنم که او هم می‌آید، اما احتمالا دیر می‌رسد

Here, the subject of می‌رسد is understood to be the same person, so there is no need to repeat او.

If you did repeat it, it would also be correct:

• من مطمئنم که او هم می‌آید، اما او احتمالا دیر می‌رسد

But that sounds more explicit than necessary.