Kull wahad is an exclamation that means "I am profoundly stirred!" It was said that Paul Atreides as Muad'Dib, upon witnessing the emergence of a young desert hawk from its shell, muttered these words.
Reverend Mother Gaius Helen Mohiam exclaimed this phrase upon administering the gom jabbar to Paul Atreides, when he managed to withstand more pain than any other Bene Gesserit student and later during their conversation when Paul assumes that the learning of the Bene Gesserit is for Politics.
Behind the Scenes
The literal Arabic meaning is "every one". (كل واحد)