to get the splashing word you need to kill the cult mages behind the door which opens with the dragon word in the deep halls near nottle's prison. there is a portal there which will take you to the room with the splashing word.
i'm not sure if u have to have gone to the City Heights yet but since ur there it doesn't matter. Go back to the ... err... Halls of Light i think and there should be 2 doors where the Cruel Glyph is marked rite? In front of them (for me, i went to the eastern door), there will be orogs who asks something of you. i agreed so they taught me the dragon word. not sure what happens when u refuse.
"Listen to your heart, but be wary of that dark corner." - Galen Blackwood
Im not sure, too, but i think the dragon word u get from orogs, to help them against cult fighting to get the helm cleaver. They ask for help, u help, say u want the cleaver too, fight against their champion in southern room and get helm cleaver!
Or not???