الكباية دي صغيرة، بس كباية الشاي كبيرة.

In Egyptian Arabic, demonstratives like دي for this usually come after the noun:

• الكباية دي = this cup
• الراجل ده = this man

This is different from English, where this comes before the noun.

Also, دي is the feminine singular form, which matches كباية, a feminine noun.

That is normal in Egyptian Arabic. The combination:

• ال + noun + دي/ده

is a very common way to say this + noun.

So:

• الكباية دي = this cup
• literally something like the cup this

It may feel redundant to an English speaker, but it is standard in Egyptian Arabic.

In Arabic, present-tense sentences like X is small usually do not need a verb equivalent to is.

So:

• الكباية دي صغيرة = This cup is small
• كباية الشاي كبيرة = The teacup is big

This is called a nominal sentence. Arabic simply puts the subject and the description together, without a present-tense copula.

Because صغيرة here is a predicate, not an adjective inside the noun phrase.

Compare these:

• الكباية الصغيرة = the small cup
  Here الصغيرة directly describes the noun, so it takes الـ too.

• الكباية دي صغيرة = this cup is small
  Here صغيرة is the predicate: it tells you something about the cup. Predicate adjectives in this kind of sentence are normally indefinite, so they do not take الـ.

The same thing happens in:

• كباية الشاي كبيرة = the teacup is big

Because they are agreeing with كباية, which is a feminine singular noun.

In Arabic, adjectives usually agree with the noun in gender and number. So:

• feminine singular: صغيرة, كبيرة
• masculine singular: صغير, كبير

For example:

• الولد صغير = the boy is small
• البنت صغيرة = the girl is small

Since كباية is feminine, the adjectives must be feminine too.

Because this is a possessive/construction phrase, often compared to the iḍāfa structure.

In this structure:

• the first noun usually does not take الـ
• the second noun can make the whole phrase definite

So:

• كباية الشاي = the tea cup / the cup of the tea
• not الكباية الشاي

This is similar to how Arabic often expresses possession or close noun relationships by putting two nouns next to each other.

When كباية comes before another noun in this kind of construction, the final ـة is often pronounced more like -et rather than just -a.

So you may hear:

• كباية alone: kobbaaya or kobaya
• كباية الشاي: kobbaayet eš-šāy

This happens because the word is linked directly to the noun after it.

Also, الشاي is pronounced eš-šāy, not el-shāy, because ش is a sun letter, so the ل of الـ assimilates in pronunciation.

It depends on context, which is why learners often ask about it.

• كباية الشاي can mean the tea cup / the teacup
• كباية شاي often means a cup of tea

In your sentence, since the meaning has already been given to the learner, you should follow that intended meaning. But in real life, context is very important with phrases like this.

So the difference is often:

• كباية شاي = a cup of tea
• كباية الشاي = the tea cup / the cup for the tea / the tea’s cup, depending on context

Here بس means but:

• الكباية دي صغيرة، بس كباية الشاي كبيرة
• This cup is small, but the teacup is big

In Egyptian Arabic, بس is very common in speech.

Be aware that بس can also mean only or just in other contexts, so its meaning depends on the sentence.

Yes. If you say:

• الكباية صغيرة

that means The cup is small.

If you say:

• الكباية دي صغيرة

that means This cup is small.

So دي adds the idea of this. Without it, the sentence is still correct, but the meaning becomes less specific.

A few things make it sound clearly colloquial/Egyptian rather than Modern Standard Arabic:

• دي as the feminine this
• بس for but
• كباية as a very common everyday word for cup

In Modern Standard Arabic, you would expect something more like:

• هذا/هذه
• لكن
• possibly كوب depending on context

So this sentence is natural everyday Egyptian Arabic, not formal written Arabic.