Χτες άκουσα έναν δυνατό κεραυνό και η γάτα κρύφτηκε κάτω από το κρεβάτι.

Yes. Χτες and χθες both mean yesterday.

• χθες is the more traditional spelling
• χτες is a very common modern spelling that reflects the actual pronunciation more closely

In everyday speech, many Greeks say χτες. So this sentence is completely natural.

A rough pronunciation guide is:

Htes A-kou-sa e-nan dha-na-TO ke-ra-vno ke i GA-ta KRI-fti-ke KA-to a-PO to kre-VA-ti

A few useful points:

• χ sounds like a rough h / kh sound, not like English ch
• αι is pronounced e
• ου is pronounced oo
• γ before α is like a soft voiced sound, similar to English g in some contexts, but often smoother
• The written accent shows which syllable is stressed:
  • άκουσα
  • δυνατό
  • κεραυνό
  • γάτα
  • κρύφτηκε
  • από
  • κρεβάτι

Because άκουσα is the simple past form, while ακούω means I hear / I am hearing in the present.

• ακούω = I hear
• άκουσα = I heard

In this sentence, the action happened yesterday, so Greek uses the past form:

• Χτες άκουσα... = Yesterday I heard...

This is the aorist form, which is very commonly used for completed past actions.

Because Greek often leaves out subject pronouns when they are clear from the verb ending.

• άκουσα already means I heard
• so εγώ άκουσα would only be used for emphasis, like I heard

This is very normal in Greek. The verb ending often tells you who the subject is.

Because this whole phrase is the direct object of άκουσα.

The verb ακούω / άκουσα takes an object, and in Greek the direct object usually goes in the accusative case.

Here:

• έναν = masculine accusative singular of ένας
• δυνατό = masculine accusative singular of δυνατός
• κεραυνό = masculine accusative singular of κεραυνός

They all match because:

• the noun is masculine
• singular
• accusative

So Greek is showing grammatical relationships through word endings.

Because κεραυνός is a masculine noun.

Greek indefinite articles change for gender:

• ένας = masculine
• μία / μια = feminine
• ένα = neuter

Since κεραυνός is masculine, the accusative form is έναν.

So:

• ένας κεραυνός = a thunderclap / a bolt of lightning
• άκουσα έναν κεραυνό = I heard a thunderclap

κεραυνός can mean lightning bolt, thunderbolt, or sometimes the striking event itself. In many contexts, especially in sentences like this, it can sound natural to translate it as a loud thunderclap depending on the meaning being given.

A learner should know this:

• βροντή is the more straightforward word for thunder
• αστραπή is lightning
• κεραυνός often refers to the lightning strike / thunderbolt, but in everyday understanding it may overlap with the dramatic sound/event

So the exact English translation can vary a little depending on context.

Yes, literally δυνατός often means strong, but it is also used to mean loud with sounds.

So:

• δυνατός ήχος = loud sound
• δυνατή μουσική = loud music
• δυνατός κεραυνός = loud / powerful thunderclap or thunderbolt

This is very natural Greek usage.

Because η γάτα is the subject of the second clause.

Compare:

• η γάτα = the cat → nominative, used for the subject
• τη γάτα = the cat → accusative, used for the object

In this sentence:

• η γάτα κρύφτηκε = the cat hid

The cat is doing the action, so Greek uses the nominative form η γάτα.

Because Greek normally uses the article with nouns much more regularly than English does.

So Greek naturally says:

• και η γάτα κρύφτηκε = and the cat hid

Even though English might sometimes sound smoother with a slightly different rhythm, in Greek this is completely standard.

κρύφτηκε is the simple past, 3rd person singular form of κρύβομαι, which means I hide or I hide myself / I get hidden, depending on context.

Here it means:

• κρύφτηκε = he/she/it hid

Since η γάτα is singular, the verb is singular too.

This is a very common kind of Greek verb where the dictionary form is in -ομαι, but it can have an active meaning in English:

• κρύβομαι = I hide / I hide myself
• κρύφτηκα = I hid
• κρύφτηκε = he/she/it hid

Because with verbs like κρύβομαι, the reflexive idea is already built into the verb.

So Greek does not need to say a separate word equivalent to itself here.

• η γάτα κρύφτηκε naturally means the cat hid
• depending on English style, that can also be understood as the cat hid itself

Greek often expresses this meaning through the verb form alone.

κάτω από means under / underneath / below.

It is a very common expression:

• κάτω = down / below
• από = from, but in this combination it helps form the meaning under

So:

• κάτω από το κρεβάτι = under the bed

This is a fixed and very common phrase in Greek.

It does, but here the noun is neuter, and the nominative and accusative forms are often identical in neuter nouns.

The preposition από takes the accusative:

• το κρεβάτι can be nominative or accusative in form
• here it is accusative because it follows από

So although the form looks unchanged, grammatically it is functioning as accusative.

The given word order is very natural, but Greek word order is more flexible than English.

This sentence:

• Χτες άκουσα έναν δυνατό κεραυνό και η γάτα κρύφτηκε κάτω από το κρεβάτι

is a neutral, everyday way to say it.

Greek could move some elements for emphasis, for example:

• Η γάτα κρύφτηκε κάτω από το κρεβάτι χτες, όταν άκουσα έναν δυνατό κεραυνό
• Χτες η γάτα κρύφτηκε κάτω από το κρεβάτι όταν άκουσα έναν δυνατό κεραυνό

Not every rearrangement sounds equally natural, but Greek definitely allows more freedom than English because cases and verb endings help show the relationships.

Yes, here και simply means and.

It links the two past events:

• άκουσα έναν δυνατό κεραυνό
• η γάτα κρύφτηκε κάτω από το κρεβάτι

So the structure is:

• Yesterday I heard a loud thunderclap, and the cat hid under the bed

Very straightforward.

Yes, absolutely:

• Χθες άκουσα έναν δυνατό κεραυνό και η γάτα κρύφτηκε κάτω από το κρεβάτι.

That is equally correct. The difference is mainly spelling style and register, not meaning.