Ne trompu.

In Esperanto, -u is the verb ending used for a command, request, wish, or instruction. It is often called the volitive form.

So:

• trompi = to deceive / to cheat
• trompas = deceives / is deceiving
• trompu = deceive! / should deceive / let ... deceive

In Ne trompu, the -u form makes it a command: Don’t deceive or Don’t cheat.

Ne is the normal Esperanto word for not.

It goes before the word or phrase it negates. In this sentence, it negates the command:

• Trompu. = Deceive! / Cheat!
• Ne trompu. = Don’t deceive! / Don’t cheat!

So ne is simply making the command negative.

Yes, the subject is omitted, and that is very normal in commands.

In English, we also usually leave out you in commands:

• Sit down.
• Don’t move.

Esperanto does the same thing:

• Trompu.
• Ne trompu.

The understood subject is usually you. So Ne trompu means You, don’t deceive or simply Don’t deceive.

It can mean either one person or more than one person.

Esperanto vi normally covers both singular and plural you, and when the subject is omitted in a command, the same idea applies. So Ne trompu could be said to:

• one person
• several people

If needed, context makes it clear.

Yes, you can, but normally Ne trompu is more natural.

Adding vi is possible for emphasis or contrast:

• Vi ne trompu, sed li helpu. = You shouldn’t deceive, but he should help.

In ordinary direct commands, Esperanto usually leaves the subject out, just like English often does.

Because -as is the present tense, not the command form.

Compare:

• Vi ne trompas. = You are not deceiving / You do not deceive
• Ne trompu. = Don’t deceive

So if you want a negative statement, use -as.
If you want a negative command, use ne + -u.

The dictionary form is trompi, which is the infinitive and means to deceive, to cheat, or to trick, depending on context.

The parts are:

• tromp- = the root
• -i = infinitive ending
• -u = command/volitive ending

So trompu is the -u form of trompi.

Good question. Trompi is usually a transitive verb, so very often it does have an object:

• Ne trompu min. = Don’t deceive me.
• Li trompis siajn amikojn. = He deceived his friends.

But the object can be left out when it is general or unimportant.
So Ne trompu works fine as a broad warning or moral instruction: Don’t cheat or Don’t deceive.

A simple pronunciation guide is:

• Ne ≈ neh
• trompu ≈ TROM-poo

Stress in Esperanto falls on the second-to-last syllable, so:

• trompu → TROM-pu

So the whole sentence sounds roughly like:

NEH TROM-poo

By itself, Ne trompu is a straightforward command or prohibition. It is not automatically rude, but it is direct.

If you want to sound softer or more polite, you might say:

• Bonvolu ne trompi. = Please do not deceive.
• Mi petas, ne trompu. = I ask you, don’t deceive.

So Ne trompu is the basic direct form, while other wording can make it gentler.