Дев’ятий урок завтра.

Because дев’ятий means ninth, not nine.

In this sentence, урок is being identified by its order in a sequence, so Ukrainian uses an ordinal number:

• дев’ять = nine
• дев’ятий = ninth

So дев’ятий урок means the ninth lesson or lesson nine, depending on context.

Because дев’ятий behaves like an adjective, and it must agree with the noun урок.

Here:

• урок is masculine
• singular
• nominative

So the ordinal also takes the masculine nominative singular form:

• дев’ятий урок = the ninth lesson

If the noun changed, the ordinal would change too. For example:

• дев’ята сторінка = the ninth page
• дев’яте завдання = the ninth task

In Ukrainian, the verb to be is often omitted in the present tense.

So:

• Дев’ятий урок завтра.

literally looks like:

• Ninth lesson tomorrow.

but naturally means:

• The ninth lesson is tomorrow.

This is completely normal Ukrainian. If you included є here, it would usually sound unnatural.

Both дев’ятий and урок are in the nominative singular.

That is because урок is the subject of the sentence, and дев’ятий agrees with it.

• урок = nominative singular masculine
• дев’ятий = nominative singular masculine, matching урок

The word завтра is not a noun here, so it does not have case in this sentence. It is an adverb meaning tomorrow.

Завтра is an adverb meaning tomorrow.

It tells you when the lesson is. Ukrainian often uses time words like this without any preposition:

• сьогодні = today
• завтра = tomorrow
• вчора = yesterday

So Дев’ятий урок завтра means that the ninth lesson takes place tomorrow.

Yes. Ukrainian word order is flexible.

You could also say:

• Завтра дев’ятий урок.

This usually means the same thing: The ninth lesson is tomorrow.

The difference is mainly emphasis:

• Дев’ятий урок завтра puts a little more attention on the ninth lesson
• Завтра дев’ятий урок puts a little more attention on tomorrow

In simple everyday use, both are natural.

The apostrophe shows that the consonant before я is not softened and that the я keeps a y-like sound.

So дев’ятий is pronounced roughly like:

• dev-YA-tyy

The apostrophe is a normal spelling feature in Ukrainian. It often appears before я, ю, є, ї after certain consonants.

Without getting too technical, in this word it helps show the correct pronunciation and spelling.

A rough pronunciation is:

dev-YA-tyy u-ROK ZAV-tra

Approximate stress:

• дев’я́тий
• уро́к
• за́втра

Stress is important in Ukrainian, but it is usually not written in normal text.

It can mean either, depending on context.

Урок often means:

• a lesson
• a class period in school

So дев’ятий урок завтра could be understood as:

• The ninth lesson is tomorrow or
• The ninth class is tomorrow

The exact English translation depends on the situation.

Yes, you could.

Дев’ятий урок буде завтра explicitly includes the future form буде = will be.

That version can sound more explicit or a bit more formal:

• Дев’ятий урок завтра. = The ninth lesson is tomorrow.
• Дев’ятий урок буде завтра. = The ninth lesson will be tomorrow.

In many everyday situations, the shorter version without буде is more natural.