When I first watched the film, I was under the impression that Muad'Dib was shouting Chaaaaar-ge!. But when I watched it again much later, that didn't seem to fit as the second syllable sounds different. I've seen some subtitles transcribe it as Chaaak-saa! (or similar).
Paul: Orato! This obelisk is of your hardest stone... Kick it.
Paul: Hit it.
Paul: Yell at it. (Troops laugh)
Paul: Cut it.
Paul: Move back.
Paul: This is part of the weirding way that we will teach you. Some thoughts have a certain sound, that being equivalent to a form. Through sound and motion, you will be able to paralyse nerves, shatter bones, set fires, suffocate an enemy or burst his organs. We will kill until no Harkonnen breathes Arrakeen air.
Fremen soldier: Chuk...sa!
Fremen soldier: Muad'dib! (Echoes)
Paul (voiceover): My name is a killing word. They are ready to fight, yet in order to lead them I must conquer the world, conquer Shai-Hulud.
The killing word is used in tandem with the weirding module (which only exists in the movie):
Director David Lynch is said to have adapted the weirding way into the Weirding Module because he did not like the idea of "Kung-fu on sand dunes". The change literalizes Paul's line "My own name is a killing word." In the novel, the Fremen shout his Fremen name, "Muad'Dib," as a battle cry; in the film, the Fremen are surprised to find that saying "Muad'Dib" is a powerful trigger for the Weirding Module.
So, the Fremen find that Muad'Dib itself is a killing word. Chani is not a killing word in either medium/version.