الذهب ثقيل.

In careful MSA pronunciation, it is adh-dhahab(u), not al-dhahab.

Why? Because the الـ in الذهب contains the definite article al-, and the letter ذ is a sun letter. With sun letters, the l sound of al- assimilates to the next consonant.

So:

• الذهب → adh-dhahab
• fully vocalized in context: الذَّهَبُ

A rough pronunciation guide:

• dh = like th in this
• so ذهب sounds roughly like dhahab

Because Arabic normally does not use a present-tense verb meaning to be in simple sentences like this.

So:

• الذهب ثقيل = Gold is heavy
• literally: Gold heavy

This is completely normal in Arabic. This kind of sentence is called a nominal sentence.

If you wanted the past tense, then Arabic would use a verb, for example:

• كان الذهب ثقيلاً = The gold was heavy

It is adjective-like in meaning, but in this sentence it is functioning as the predicate of the sentence, not as an attributive adjective attached inside a noun phrase.

So in:

• الذهب ثقيل = Gold is heavy

الذهب is the topic/subject, and ثقيل is the predicate: it tells you something about gold.

Compare that with a true noun + adjective phrase:

• الذهب الثقيل = the heavy gold

There, الثقيل is a regular adjective describing الذهب, and it must match it in definiteness.

Because Arabic usually puts the predicate after the subject/topic in this kind of simple nominal sentence.

So the normal order is:

• الذهب = the subject/topic
• ثقيل = the predicate

This is the standard way to say Gold is heavy.

Because الذهب means gold as a definite or generic noun here, while ثقيل is the predicate.

In Arabic nominal sentences, it is very common for:

• the subject/topic to be definite
• the predicate to be indefinite

So:

• الذهب = the gold / gold as a known class or substance
• ثقيل = heavy

If you said:

• الذهب الثقيل

that would no longer mean Gold is heavy. It would mean the heavy gold.

Because Arabic often uses the definite article with nouns when speaking about something generically.

So الذهب can mean:

• the gold
• or more naturally in English, just gold

English and Arabic do not always use definiteness in the same way. In English, we usually say:

• Gold is heavy

not:

• The gold is heavy

unless we mean some specific gold.

The fully vowelled form is:

• الذَّهَبُ ثَقِيلٌ

This shows the normal case endings for an unpaused sentence:

• الذَّهَبُ = adh-dhahabu
• ثَقِيلٌ = thaqīlun

In everyday printed Arabic, these short vowels are usually omitted, so you normally see:

• الذهب ثقيل

Because if you added الـ and said:

• الذهب الثقيل

you would get a noun phrase meaning:

• the heavy gold

That is different from:

• الذهب ثقيل = Gold is heavy

This is an important pattern in Arabic:

• noun + indefinite adjective/predicate can form a sentence
• noun + definite adjective usually forms a noun phrase

So the lack of الـ on ثقيل helps show that this is a complete sentence, not just a phrase.

Because الذهب is grammatically masculine in Arabic, so the predicate uses the masculine singular form:

• ثقيل = masculine singular
• feminine would be ثقيلة

Arabic words must agree in gender when appropriate, and predicates commonly match the noun in gender and number.

It is grammatically singular.

Even though gold is a substance noun in English, Arabic treats الذهب as a singular noun. That is why the predicate is also singular:

• الذهب ثقيل
• not a plural form of heavy

ثقيل literally means heavy.

It comes from a root related to heaviness or weight. In different contexts, it can also be used more figuratively, such as meaning:

• burdensome
• weighty
• hard to bear

But in this sentence, the meaning is simply physical:

• Gold is heavy

A natural careful reading would be:

• adh-dhahabu thaqīlun

If you pause at the end, as speakers usually do, the final case endings are often not fully pronounced, so you may hear something closer to:

• adh-dhahab thaqīl

Both reflect the same written sentence:

• الذهب ثقيل

A common MSA way is:

• الذهب ليس ثقيلاً = Gold is not heavy

Here:

• ليس is used for negating this kind of present-time statement
• ثقيلاً takes the accusative ending in fully vocalized Arabic

In ordinary unvocalized writing, you would usually just see:

• الذهب ليس ثقيلاً or الذهب ليس ثقيلًا

It is a nominal sentence: جملة اسمية.

Its two main parts are:

• المبتدأ: الذهب
• الخبر: ثقيل

In simple terms:

• الذهب = what you are talking about
• ثقيل = what you say about it

This is one of the most basic and important sentence patterns in Arabic.