المتحدث جاهز للكلمة الرئيسية.

It is a nominal sentence in Arabic, meaning it starts with a noun rather than a verb.

• المتحدث = the subject
• جاهز = the predicate/complement
• للكلمة الرئيسية = a prepositional phrase explaining what the speaker is ready for

Arabic often uses this kind of structure to express a present-time idea, so there is no separate word for is here. The sentence literally works like:

• The speaker ready for the keynote/main speech

In natural English, we add is: The speaker is ready for the keynote speech.

المتحدث means the speaker or the person speaking.

It comes from the root ح د ث, which is related to speaking, talking, or happening in different forms. In this sentence, المتحدث is a noun referring to a person: the speaker.

Without الـ, متحدث would mean a speaker or someone speaking.

الـ is the Arabic definite article, equivalent to the in English.

So:

• متحدث = a speaker
• المتحدث = the speaker

Since the sentence is talking about a specific speaker, Arabic uses الـ.

Because جاهز here is not another noun meaning the ready one. It is functioning as the predicate of the sentence: ready.

In Arabic nominal sentences, it is very common for the subject to be definite and the predicate to be indefinite:

• المتحدث جاهز = The speaker is ready

If you said المتحدث الجاهز, that would usually mean the ready speaker, a noun phrase rather than a full sentence.

Yes, جاهز is an adjective meaning ready.

In this sentence, it describes the state of المتحدث. Because the speaker is masculine singular, جاهز is also in the masculine singular form.

Compare:

• المتحدث جاهز = The speaker is ready (masculine)
• المتحدثة جاهزة = The female speaker is ready (feminine)

The لِـ is a preposition, and here it means something like for.

So:

• جاهز للكلمة الرئيسية = ready for the keynote/main speech

This is a common pattern in Arabic:

• جاهز لِـ... = ready for...

Because لِـ is attached to a word that already begins with الـ, the spelling becomes لِلـ written together as للـ.

So للكلمة is basically:

• لِ + الكلمة → للكلمة

Because الرئيسية is an adjective modifying الكلمة, and in Arabic adjectives must match the noun they describe in definiteness, as well as gender and number.

Since الكلمة is definite (the word / the speech), the adjective must also be definite:

• الكلمة الرئيسية = the main/key word or the keynote speech
• كلمة رئيسية = a main/key word

This matching is very important in Arabic adjective phrases.

Because it describes الكلمة, and كلمة is a feminine noun in Arabic.

So the adjective must agree with it:

• كلمة رئيسية = feminine singular
• كتاب رئيسي = masculine singular

Even if the overall meaning in English might be something abstract, the grammar follows the gender of the Arabic noun.

A couple of pronunciation points matter here:

• الرئيسية: the ر is a sun letter, so the ل of الـ is not pronounced separately. It sounds like ar-ra’īsiyyah, not al-ra’īsiyyah.
• للكلمة: this is pronounced roughly lil-kalimah or lil-kalimati in careful reading, because it comes from لِ + الكلمة.

So a careful pronunciation of the whole sentence is approximately:

al-mutahaddith jāhiz lil-kalimah ar-ra’īsiyyah

Yes, in fully vocalized formal Arabic, the words would show case:

• المتحدثُ = nominative, because it is the subject
• جاهزٌ = usually nominative as the predicate
• لِلكلمةِ = genitive after the preposition لِ
• الرئيسيةِ = genitive too, because it follows الكلمة and agrees with it

In normal everyday writing, these endings are usually not written, so you see:

المتحدث جاهز للكلمة الرئيسية

But in careful grammatical analysis, the case is still there.

Yes. Depending on context, الكلمة الرئيسية can mean:

• the keynote speech
• the main speech
• the key word / keyword

Arabic often relies on context to decide which meaning is intended. So if this sentence appears at a conference, it probably means the keynote speech. In another context, it could mean the keyword or main word.

Yes. Arabic word order is flexible, although the most neutral version here is:

المتحدث جاهز للكلمة الرئيسية

You could also say:

المتحدث للكلمة الرئيسية جاهز

but that is less natural in many contexts and may sound more marked or literary. For a learner, the original order is the best one to use.