Chumba cha abiria ni kikubwa.

Because cha has to agree with chumba, not with abiria.

In Swahili, the -a possessive/genitive connector changes form depending on the noun class of the noun before it.
Chumba belongs to the ki-/vi- class, so the connector becomes cha.

So:

• chumba cha abiria = room of the passenger / passenger room

If the first noun were from a different noun class, the connector would change:

• nyumba ya abiria = the passenger’s house
• kitabu cha mwanafunzi = the student’s book

So cha is there because of chumba.

Here, cha links two nouns together. It often corresponds to English of, for, or the apostrophe ’s, depending on context.

So chumba cha abiria can be understood as something like:

• the passenger’s room
• the passengers’ room
• a passenger room / passenger cabin

The exact English wording depends on the situation, but grammatically cha is the linking word.

Ni is the copula here, meaning is / are.

So the structure is:

• Chumba cha abiria = the subject
• ni = is
• kikubwa = big

So the sentence literally works like:

• Passenger room is big

Natural English adds articles, but Swahili does not need them.

Because adjectives in Swahili usually agree with the noun class of the noun they describe.

Since chumba is in the ki-/vi- class, the adjective -kubwa takes the agreement prefix ki-, giving:

• ki + kubwa = kikubwa

So:

• chumba kikubwa = a big room
• chumba cha abiria ni kikubwa = the passenger room is big

If the noun were plural, the adjective would change too:

• vyumba ... ni vikubwa = the rooms ... are big

It can depend on context, because abiria is one of those Swahili nouns that often looks the same in singular and plural.

So abiria can mean:

• a passenger
• passengers

In this sentence, the intended meaning is usually clear from context.
Also, notice that cha still agrees with chumba, so whether abiria is singular or plural does not change cha here.

Swahili normally does not have separate words for English articles like a, an, and the.

So Chumba cha abiria ni kikubwa could be translated in different ways depending on context:

• The passenger room is big
• A passenger room is big
• The passengers’ room is big

English forces you to choose an article, but Swahili usually leaves that to context.

In this sentence, it is best to keep ni.

With ni, the sentence clearly means:

• The passenger room is big

If you remove ni, the result may sound incomplete or may feel more like a noun phrase than a full statement in standard learning contexts.

So for a simple clear sentence like this, learners should keep:

• Chumba cha abiria ni kikubwa.

The word order is:

• Subject
  • ni
    • predicate

More specifically:

• Chumba cha abiria = subject noun phrase
• ni = is
• kikubwa = adjective used as the predicate

So the pattern is very similar to English:

• The passenger room
  • is
    • big

Inside the subject, cha abiria comes after chumba because Swahili usually puts modifiers after the noun.

You would make chumba plural, and then the agreement words must change with it.

• chumba → vyumba
• cha → vya
• kikubwa → vikubwa

So the plural sentence is:

• Vyumba vya abiria ni vikubwa.

That means:

• The passenger rooms are big.

Notice that abiria usually stays the same in form.

A simple pronunciation guide is:

• Chumba = CHOOM-bah
• cha = chah
• abiria = ah-bee-REE-ah
• ni = nee
• kikubwa = kee-KOOB-wah

A few useful points:

• ch is like the ch in church
• u is like oo in food
• Swahili vowels are usually pronounced clearly and consistently
• Stress is typically on the second-to-last syllable

So you would naturally say something close to:

• choom-bah chah ah-bee-REE-ah nee kee-KOOB-wah

Yes. In Swahili, this structure often shows a general relationship, not just ownership.

So chumba cha abiria could mean a room:

• belonging to a passenger
• used by passengers
• intended for passengers

This is very common in Swahili. The -a connector can express several kinds of relationships, and context tells you which one is meant.

Chumba is in the ki-/vi- noun class:

• singular: chumba
• plural: vyumba

This matters because other words connected to chumba must agree with that class. In this sentence, that is why you get:

• cha in chumba cha abiria
• ki- in kikubwa

So noun class is the reason the sentence looks the way it does. Once you know the class of chumba, the other agreement forms make more sense.