Ρύθμισε το χρονόμετρο.

Ρύθμισε is the second-person singular imperative of ρυθμίζω, meaning it is a command addressed to one person.

So the structure is basically:

Ρύθμισε = set / adjust το χρονόμετρο = the timer

It is the form you use when telling one person to do something directly.

Greek usually does not need a separate subject pronoun in commands.

In Ρύθμισε το χρονόμετρο, the ending of Ρύθμισε already tells you that the speaker is addressing one person. So the you is understood.

You could add εσύ for emphasis, but that would sound marked:

Εσύ, ρύθμισε το χρονόμετρο.

That would mean something more like you set the timer.

This is about aspect, which is very important in Greek commands.

Ρύθμισε is the aorist imperative. It usually presents the action as a single whole action: Set it. Do it once. Get it done.

Ρύθμιζε is the present imperative. It usually suggests an ongoing, repeated, or habitual action: Keep adjusting it or adjust it regularly.

So in a normal one-time command like Set the timer, Greek naturally uses:

Ρύθμισε το χρονόμετρο.

Το is the definite article, meaning the.

It agrees with χρονόμετρο, which is a neuter singular noun. So:

το χρονόμετρο = the timer

Greek uses articles very regularly, and here it works much like English does.

It is in the accusative case, because it is the direct object of the verb.

The timer is the thing being set, so it takes the accusative.

A useful detail is that for many neuter nouns, the nominative and accusative forms are the same. So:

το χρονόμετρο can be nominative or accusative depending on its role in the sentence.

Here it is accusative because it is the object of Ρύθμισε.

There are two good clues.

First, the article is το, which is the neuter singular article.

Second, the noun ends in -ο, which is a very common neuter ending in Greek.

So from το χρονόμετρο, you can identify the noun as neuter singular.

Yes. It is very easy to connect it to familiar roots.

χρονόμετρο is built from: χρόνος = time -μέτρο = measure

So it is literally something like time-measurer.

That is related to English elements like chrono- and meter. This can make the word easier to remember.

A helpful approximation is:

REE-thmee-seh toh khroh-NOH-meh-troh

A few sound notes:

Ρ = rolled or tapped r υ here sounds like ee θ sounds like th in thin χ sounds like a rough h/kh sound, not like English ch The stress falls on ΡΥ in Ρύθμισε and on ΝΟ in χρονόμετρο

A more IPA-style pronunciation is roughly:

ˈriθmise to xroˈnometro

Yes, Greek word order is more flexible than English word order.

The most neutral version for a command is:

Ρύθμισε το χρονόμετρο.

That puts the verb first, which is very natural in instructions.

You might also hear a different order for emphasis, but it would sound less neutral. For a learner, the verb-first version is the best one to use.

You would normally use the plural imperative:

Ρυθμίστε το χρονόμετρο.

This can mean: Set the timer when speaking to more than one person or a more polite/formal command to one person

So the contrast is:

Ρύθμισε = singular, informal Ρυθμίστε = plural or polite

Not especially. It comes from the verb ρυθμίζω.

Many Greek verbs form an aorist command with a pattern like this, and the stress often shifts between forms. So the change from ρυθμίζω to Ρύθμισε may look surprising at first, but it is part of normal Greek verb formation.

So it is a form you should learn as part of the verb’s pattern:

ρυθμίζω = I set / adjust ρύθμισε = set / adjust

It is a good example of why Greek verbs are best learned with a few key forms, not just one dictionary form.