القاعدة غير مستوية.

In Arabic, the present tense of to be is usually not stated in simple sentences like this.

So القاعدة غير مستوية literally looks like:

• the base/foundation
• not level

But it means The base is uneven / not level.

This is called a nominal sentence in Arabic. In the present tense, Arabic normally leaves out is/am/are.

القاعدة can have more than one meaning depending on context. Common meanings include:

• base
• foundation
• rule

In this sentence, because it is followed by غير مستوية (not level / uneven), the most natural meaning is the base or the foundation, not the rule.

So context is what tells you which meaning is intended.

Yes. The ending ـة (taa marbuuTa) usually marks a noun as feminine.

So القاعدة is grammatically feminine. Because of that, anything describing it must also be feminine. That is why you get مستوية rather than a masculine form.

This is a very common pattern in Arabic:

• feminine noun → feminine adjective

Because adjectives in Arabic must agree with the noun they describe in:

• gender
• number
• definiteness

Since القاعدة is:

• feminine
• singular
• definite

the describing word must match appropriately.

Here, the adjective inside the phrase is مستوية, the feminine singular form of مستوٍ / مستوي meaning level, even, flat.

غير is a very common way to express not or non- before adjectives and nouns.

So:

• مستوية = level / even
• غير مستوية = not level / uneven

In many cases, غير + adjective works like an English adjective with un- or not.

Examples:

• مفيد = useful
• غير مفيد = not useful

So here غير مستوية means uneven or not level.

Yes, there is a special point.

غير behaves like a noun in a kind of construct phrase. The word after it is grammatically linked to it. So in fully vocalized Arabic, the ending of مستوية would reflect that relationship.

That means this is not exactly the same as simply putting a negative particle before an adjective in English. It is a fixed and very common Arabic pattern:

• غير + adjective
• غير + noun

Even if you do not study the full case grammar yet, it is very useful to recognize غير as a standard way to form meanings like:

• not X
• non-X
• un-X

Because in Arabic, adjectives normally come after the nouns they describe.

So Arabic says the equivalent of:

• the base uneven

rather than:

• the uneven base

or:

• the base is uneven

depending on the sentence structure.

That is normal Arabic word order.

Because the sentence is structured as:

• القاعدة = the subject, definite
• غير مستوية = the predicate, which is typically indefinite

In simple Arabic sentences like The house is big or The road is long, it is normal for the subject to be definite and the predicate to be indefinite.

Compare:

• البيت كبير = The house is big
• القاعدة غير مستوية = The base is uneven

So the lack of الـ on the predicate is normal.

Yes. That is also correct.

• القاعدة غير مستوية
• القاعدة ليست مستوية

Both can mean The base is not level.

A rough difference is:

• غير مستوية feels like a descriptive quality: uneven
• ليست مستوية is a more direct verbal negation: is not level

In many contexts, either one works. Learners should recognize both patterns.

The base masculine form is مستوٍ or in less formal unvowelled writing often مستوي.

Its feminine form is مستوية.

It comes from the verb استوى, which can carry meanings related to:

• becoming level
• being even
• becoming settled or straight

So مستوية here means level / even / flat in the feminine singular form.

A careful full reading is approximately:

al-qaaʿidatu ghayru mustawiyatin

In normal pause, learners often hear or say something closer to:

al-qaaʿidah ghayr mustawiyah

A few pronunciation notes:

• ق is a deep q sound, not an English k
• ع is a throat sound with no exact English equivalent
• غ in غير is like a voiced French/German-style r sound in the throat

If you are a beginner, the most important thing is to recognize the words and the overall rhythm of the sentence.

In fully vowelled formal Arabic, it would be:

الْقَاعِدَةُ غَيْرُ مُسْتَوِيَةٍ

Why?

• القاعدةُ is the subject of the nominal sentence, so it is nominative
• غيرُ is the predicate, also nominative
• مستويةٍ comes after غير in the grammatical relationship associated with it, so it takes a genitive ending

Many learners first meet this sentence without case endings, which is completely normal in everyday printed Arabic.