Fires an impacted object into the air.
Waddiwasi is a charm that removes impacted objects and launches them through the air at the will of the caster.
Hogwarts professor, Remus Lupin used this to dislodge a wad of gum that had been shoved in a keyhole in attempt to block it by Peeves. After casting his spell, the gum went rocketting up Peeves' nose.
Behind the scenes
Latin vade, "travel." Possibly Swedish vadd, meaning "soft mass" (in this case, gum); or French vas y, "go there," as Lupin also directed the object upwards; or possibly from the English wad, as in "a wad of gum". Waddiwasi may also be a combination of the words wad and kamikaze. In this case, the spell's function is most likely to be as simple as causing a wad of something to launch itself sacrificially at someone nearby. As the perfect spitball launcher, such a charm would doubtless have been a favorite tool in the arsenal of troublemakers like Moony, Wormtail, Padfoot and Prongs.