denunci

It is narrower than English denounce. The Reta Vortaro defines denunci as sciigi aŭtoritatulon aŭ la publikon pri ies krimo aŭ kulpo - to tell an authority, or the public, about somebody's crime or fault. So there has to be a wrongdoer, and there has to be somebody in a position to act. English denounce has drifted much wider: you can denounce a policy, a budget, a film. In Esperanto that is kritiki or publike kondamni, and using denunci for it will read as though you have reported the budget to the police.

The register is not neutral, and it should not be. Denunci is what a collaborator does, and the derivations make the judgement explicit: denunco is the act or the accusation itself, denuncanto is the person who did it once, and denuncisto is the one who does it as a job - the paid informer, the man planted in the room. That last suffix is the whole moral distinction. -Ist- marks a trade, and Esperanto uses it here in the same dry way English does in informer. Set the word beside perfidi, to betray: perfidi is about the broken bond, denunci about the report that broke it.

Useful next to it. Akuzi is to accuse, and it happens in the open, usually to somebody's face. Kondamni is to condemn, which is a verdict rather than a report. Informi is the neutral option when nobody has done anything wrong - informi la policon is what a witness does. And where the report is true and the cause is just, Esperanto still says denunci: the word names the act, not its morality, which is why the sentence around it has to carry the judgement.