Learn Arabic (Modern Standard): الجبل كبير والبحر واسع.

This is a classic Arabic nominal sentence. The subject الجبل (the mountain) is definite because it starts with ال, but the describing word كبير (big) is indefinite and has no ال. When a definite noun is followed by an indefinite adjective, Arabic implies the word 'is' between them. If it meant 'the big mountain', both words would need to have ال.

What is the grammatical role of the indefinite words كبير and واسع here?

They act as the predicate, which means they provide the actual news or information about the subject. In Arabic grammar, this is called the Khabar. Because they act as the predicate in a basic nominal sentence, they must be written in the indefinite form.

How does the Tanween ending apply to كبير and واسع in this sentence?

Because these words are indefinite, they take a special ending in formal Arabic called Tanween. For basic sentences like this, it adds an '-un' sound to the end of the word. So, كبير is formally pronounced 'kabirun' and واسع is pronounced 'wasi'un'.

Why is the word for 'and' joined directly to the word for 'the sea' as والبحر?

The Arabic word for 'and' is the single letter و (wa). In Arabic, single-letter words never stand alone with a space after them. They must always attach directly to the beginning of the following word.