The symbolic definition is broader in complexity.
It is part the chosen name of manhood that Paul Atreides selects when he is accepted into the Fremen. It is one of two names that Paul maintains within the tribe. Stilgar explains that the first, Usul, means "strength of the base of the pillar". That it is his secret name, his troop name, that only Sietch Tabr may use and none other may presume.
The second name, Muad'Dib, is that by which he is known openly. Paul's choice of the name pleased and impressed Stilgar, and other Fremen of Sietch Tabr.
- "Muad'Dib is wise in the ways of the desert. Muad'Dib creates his own water. Muad'Dib hides from the sun and travels in the cool night. Muad'Dib is fruitful and multiplies over the land. Muad'Dib we call 'instructor-of-boys.' That is a powerful base on which to build your life, Paul-Muad'Dib."
Although the English pronounciation of this word calls for a long "i", there is an almost exact word in Arabic like it (Mu'adib), which means "private tutor" or "teacher". It used to be that the Caliphs, the rulers of the Muslim world, would hire a Mu'adib to teach their children. The practice seemed to be common for other strata of society as well.
Paul is reluctant to throw away his full past and get rid of the full name his father gave him, which is why he first wished to be called Paul-Muad'Dib. Unfortunately, this name was soon forgotten and became simply "Muad'dib". Also, it was hoped that by keeping the name his father gave him, he could prevent the mass slaughter that would occur later in his name. Sadly, it was not.
The meanings of both Usul and Muad'Dib have powerful ramifications and loads of foreshadowing for the purpose Paul has on Arrakis.
Paul was instructed to take a Fremen word as his new name. While lost in the deep desert prior to being intercepted by Stilgar and his clan, Paul had spotted a small but nimble creature foraging on a rock outcrop. The creature had been a desert mouse. Upon asking the name of the creature, and being told it was called "Muad'Dib" by the Fremen, he chose it as his new name.
Paul's choice in name was also marginally influenced by the prescient visions he had begun to have after arriving on Arrakis. In one recurring vision he saw throngs of Fremen chanting the word "Muad'Dib" at him in a subservient manner.