Kamusi iliyopo katika maktaba inatusaidia kufafanua maneno.

Swahili usually does not use articles like a/an/the. A noun like kamusi can mean a dictionary or the dictionary, depending on context.

So:

• kamusi = a dictionary / the dictionary
• maktaba = a library / the library

English needs articles almost all the time, but Swahili normally does not.

Iliyopo means something like that is there, that is located, or which is found.

In this sentence, kamusi iliyopo katika maktaba means the dictionary that is in the library.

So iliyopo is describing kamusi and telling you where it is.

In Swahili, relative ideas like that or which are often built into the verb form instead of being separate words.

So instead of saying something like:

• dictionary that is in the library

Swahili says:

• kamusi iliyopo katika maktaba

Here, iliyopo already includes the idea of that is located. This is very common in Swahili grammar.

Ipo means it is there / it is present / it is located as a normal verb form.

But here the verb is being used to describe a noun:

• kamusi ipo katika maktaba = the dictionary is in the library
• kamusi iliyopo katika maktaba = the dictionary that is in the library

So iliyopo is a relative form, used when the verb modifies a noun.

Kamusi belongs to the N class (often called class 9 in the singular). This matters because verbs and modifiers have to agree with the noun class.

That is why you see:

• i- in iliyopo
• i- in inatusaidia

Both of those agree with kamusi.

A very useful thing to notice is that kamusi itself does not change form, but the agreement words around it show whether it is singular or plural.

Yes. Kamusi can be both singular and plural in form. The difference is shown by agreement.

Compare:

• kamusi iliyopo ... inatusaidia = the dictionary that is ... helps us
• kamusi zilizopo ... zinatusaidia = the dictionaries that are ... help us

So the noun may look the same, but the verb and relative form tell you the number.

Inatusaidia can be broken down like this:

• i- = subject marker agreeing with kamusi
• -na- = present tense
• -tu- = us
• -saidia = help

So literally it is:

• it + present + us + help

That gives the meaning it helps us.

In Swahili, object pronouns are often attached directly to the verb.

So instead of separate words like English helps us, Swahili can build the object into the verb:

• inatusaidia = it helps us

This is very normal in Swahili. Other examples are:

• ananisaidia = he/she helps me
• wanakusaidia = they help you
• kinawasaidia = it helps them (with a different noun class)

Kufafanua is the infinitive, meaning to explain, to clarify, or to define.

After -saidia (help), Swahili commonly uses the infinitive:

• kusaidia kufanya jambo = to help do something

So:

• inatusaidia kufafanua maneno = it helps us clarify/define words

This works much like English helps us understand, helps us explain, and so on.

Katika means in, inside, or within. It is a normal and slightly more formal or careful way to say in.

So:

• katika maktaba = in the library

In everyday speech, many speakers might also use kwenye in similar situations:

• kwenye maktaba

That can also mean in/at the library, depending on context.
So katika is absolutely correct, and kwenye is often more conversational.

The singular is neno, meaning word.

So:

• neno = word
• maneno = words

This is a noun from the ji/ma pattern (often called classes 5/6), where the plural often uses ma-.

More literally, it means to explain words, to clarify words, or to define words.

Depending on context, -fafanua can suggest:

• making something clear
• explaining in more detail
• defining the meaning of words

So in this sentence, the idea is that the dictionary helps people understand the meanings of words more clearly.

Yes, but the meaning or style would change a little.

With iliyopo, the sentence clearly says:

• the dictionary that is in the library

If you remove it and say:

• Kamusi katika maktaba inatusaidia kufafanua maneno

people may still understand you, but it is less explicit. Iliyopo makes the relationship clearer and more natural for the full idea the dictionary that is in the library.