Onu boşuna bekledik, çünkü toplantı çoktan iptal edilmişti.

Because Turkish beklemek takes a direct object, not a preposition like for.

• onu beklemek = to wait for him / her / it
• literally, Turkish structures it more like to wait him/her/it

So:

• Onu bekledik = We waited for him/her/it

This is a very common difference from English. Turkish often expresses things directly where English uses a preposition.

Onu is the accusative form of o.

• o = he / she / it / that
• onu = him / her / it / that one

Turkish does not mark gender in pronouns, so onu could mean:

• him
• her
• it

Only context tells you which one is meant.

Boşuna means:

• in vain
• for nothing
• needlessly
• for no reason

So Onu boşuna bekledik means we waited, but it was pointless.

A few similar examples:

• Boşuna geldim. = I came for nothing.
• Boşuna uğraşma. = Don’t bother. / Don’t try in vain.

Bekledik comes from:

• bekle- = wait
• -di = past tense
• -k = we

So:

• bekledik = we waited

You can compare:

• bekledim = I waited
• bekledin = you waited
• bekledi = he/she/it waited
• bekledik = we waited

Because Turkish usually does not need subject pronouns when the verb ending already shows the subject.

• bekledik already means we waited
• adding biz is possible, but usually only for emphasis

So:

• Bekledik = We waited
• Biz bekledik = We waited, specifically we

This is called a pro-drop language feature.

Çünkü means because.

It introduces the reason:

• Onu boşuna bekledik = We waited for him/her/it in vain
• çünkü toplantı çoktan iptal edilmişti = because the meeting had already been canceled

So the whole sentence follows a very common pattern:

• statement + çünkü
  • reason

In Turkish, çünkü often comes after the main statement, just like here.

Yes, çoktan often translates as already, but it usually has a stronger sense of:

• long before
• by that time already
• well before the relevant moment

So:

• toplantı çoktan iptal edilmişti = the meeting had already been canceled, and this happened before the waiting

It gives the sentence a sense that the cancellation was not recent at that point; it was already a done fact.

Because toplantı is the subject of the passive verb iptal edilmişti.

Compare:

• Toplantıyı iptal ettiler. = They canceled the meeting.
  Here toplantıyı is the direct object.

But in the passive:

• Toplantı iptal edildi. = The meeting was canceled.
  Here toplantı becomes the subject, so there is no accusative ending.

In your sentence:

• toplantı çoktan iptal edilmişti = the meeting had already been canceled

So toplantı is correct.

It is built from the passive form of iptal etmek.

Step by step:

• iptal etmek = to cancel
• passive: iptal edilmek = to be canceled
• edil-miş-ti = had been canceled

Breaking it down:

• edil- = passive stem
• -miş = completed/resultative past
• -ti = past reference point

Together, edilmişti gives a past in the past meaning, which is why English often translates it as had been canceled.

So:

• toplantı iptal edilmişti = the meeting had been canceled

Not necessarily. That is a very good question, because -miş can indeed mark hearsay in some contexts.

But in forms like -mişti, it often works as part of a pluperfect-like structure:

• iptal edilmişti = had been canceled

Here the most important idea is that the cancellation happened before another past event, namely bekledik.

So in this sentence, you should mainly understand edilmişti as:

• a completed earlier event
• with a resulting state already in place

Not primarily as hearsay.

The passive is used because the speaker focuses on the meeting and its state, not on who canceled it.

• Toplantıyı iptal ettiler. = They canceled the meeting.
• Toplantı iptal edilmişti. = The meeting had been canceled.

In your sentence, the important fact is simply that the meeting was no longer happening. The person or people who canceled it are irrelevant.

That is why the passive sounds natural.

They are related, but not the same.

• iptal edildi = it was canceled
• iptal edilmişti = it had been canceled

The second one places the cancellation earlier than another past event.

In your sentence:

• first, the meeting was canceled
• later, we waited in vain

So iptal edilmişti is the better form because it clearly shows that the cancellation happened before the waiting.

Yes, Turkish word order is flexible, but the version you have is very natural.

• Onu boşuna bekledik, çünkü toplantı çoktan iptal edilmişti.

Why it works well:

• Onu puts the object early
• boşuna sits near the verb as an adverb
• bekledik finishes the first clause
• the reason comes after çünkü

You could move some parts for emphasis, but the given order is smooth and standard.

Grammatically, yes, onu can mean it, but in this sentence the more natural reading is usually that onu refers to a person or expected participant, while toplantı refers separately to the meeting.

So the likely idea is:

• we waited for someone
• but the meeting had already been canceled

However, Turkish itself does not force that interpretation through grammar alone. Context decides.