Η πινακίδα κυκλοφορίας είναι καθαρή.

Η is the feminine singular definite article in the nominative case, so here it means the.

It matches πινακίδα, which is a feminine singular noun:

• η πινακίδα = the plate / the sign

In Greek, articles are used very often, more often than in English in some contexts.

Because πινακίδα by itself is a general word meaning sign, plate, or plaque, depending on context.

πινακίδα κυκλοφορίας is a fixed expression meaning license plate / number plate.

Literally, it is something like:

• πινακίδα = plate/sign
• κυκλοφορίας = of circulation / of traffic / for road use

So the whole phrase identifies the specific kind of plate.

κυκλοφορίας is in the genitive singular.

This is very common in Greek when one noun defines another noun, similar to English of ...:

• πινακίδα κυκλοφορίας = plate of circulation/traffic → license plate

The base noun is κυκλοφορία:

• nominative: η κυκλοφορία
• genitive: της κυκλοφορίας

So here Greek uses a noun + genitive structure instead of an adjective.

είναι is the 3rd person singular present of είμαι = to be.

So here it means is:

• Η πινακίδα κυκλοφορίας είναι καθαρή.
• The license plate is clean.

Useful comparison:

• είμαι = I am
• είσαι = you are
• είναι = he/she/it is, and also they are

Greek uses the same form είναι for both is and are in the present tense.

Because the adjective has to agree with the noun it describes.

πινακίδα is:

• feminine
• singular
• nominative

So the adjective must also be:

• feminine
• singular
• nominative

That is why we get:

• masculine: καθαρός
• feminine: καθαρή
• neuter: καθαρό

So:

• ο δρόμος είναι καθαρός = the road is clean
• η πινακίδα είναι καθαρή = the plate is clean
• το αυτοκίνητο είναι καθαρό = the car is clean

Not always. καθαρός / καθαρή / καθαρό can mean:

• clean
• clear
• pure

In this sentence, with πινακίδα κυκλοφορίας, it most naturally means clean, but it can also suggest clear and easy to read, depending on context.

So for a license plate, καθαρή may imply:

• not dirty
• not obscured
• clearly visible

Here is the breakdown:

• Η → feminine singular nominative article
• πινακίδα → feminine singular nominative
• κυκλοφορίας → feminine singular genitive
• είναι → verb
• καθαρή → feminine singular nominative adjective

Why nominative for πινακίδα and καθαρή? Because πινακίδα is the subject, and καθαρή is a predicate adjective describing that subject after είναι.

Yes. Greek word order is more flexible than English.

The neutral, straightforward order is:

• Η πινακίδα κυκλοφορίας είναι καθαρή.

But you might also hear:

• Καθαρή είναι η πινακίδα κυκλοφορίας.
• Η πινακίδα κυκλοφορίας καθαρή είναι. (more marked, less neutral)

These alternatives change the emphasis, not the core meaning.

For learners, the original order is the best one to use first.

Usually, in a normal sentence like this, you would keep it.

• Η πινακίδα κυκλοφορίας είναι καθαρή. = The license plate is clean.

If you remove the article:

• Πινακίδα κυκλοφορίας είναι καθαρή

that sounds unnatural in ordinary standard Greek unless there is some special context or stylistic reason.

Greek generally likes the article with specific nouns.

You would normally say:

• Μια πινακίδα κυκλοφορίας είναι καθαρή.

Here μια means a / one.

So:

• η πινακίδα = the license plate
• μια πινακίδα = a license plate

A rough pronunciation guide is:

ee pee-nah-KEE-tha kee-klo-fo-REE-as EE-ne ka-tha-REE

A few notes:

• η / ι / υ / ει / οι often sound like ee
• δ sounds like the th in this
• θ sounds like the th in think
• the stress matters:
  • πινακίδα
  • κυκλοφορίας
  • καθαρή

Just add δεν before the verb:

• Η πινακίδα κυκλοφορίας δεν είναι καθαρή.
• The license plate is not clean.

This is the standard way to negate a sentence with είναι.

It is widely understood, but vocabulary can vary a little by region.

In Greece, πινακίδα κυκλοφορίας is the normal formal term for license plate / registration plate.

In everyday English, learners may think of:

• license plate in American English
• number plate in British English

Greek πινακίδα κυκλοφορίας covers that idea.