You can't have a book without words (duh). You also can't have language (double duh). They're kind of the building blocks of the whole thing.
But could you have humanity without words?
The Congolese don't think so. Nelson teaches Adah the concepts of muntu, kintu, kuntu, and nommo. Like everything in Congolese, these words have multiple meanings. Muntu can mean man or people (as in "mankind" not as in "human with male genitalia"). But the word muntu makes "no special difference between living people, dead people, children not yet born, and gods" (3.2.3). In other words, it's a special kind of life force that makes us, us.
Kintu is pretty much any other being or concept. A bird, a place, a time, a rock, a toilet seat. All kintu. "'All that is being here, ntu,' says Nelson with a shrug, as if this is not so difficult to understand" (3.2.3). Umm, we have a headache. A headache is probably kintu too. If we understand this correctly, and we probably don't, any -ntu has the potential for life, or existence.
Little Nommo, the Word Master
To make matters more complicated, we have nommo. "Nommo means word" (3.2.3). Something is not considered "alive" until it has been named, not even a child. This not only harkens back to the story of Genesis, in which Adam names the animals, but also something Leah said back in Book 2: "In the beginning we were just about in the same boat as Adam and Eve. We had to learn the names of everything" (2.1.1).
But what if you named something wrong? Would that change its existence? Even Shakespeare said, "that which we call a rose/By any other name would smell as sweet."
But what if it were called the Poopflower? Adah says, "If you assign the wrong names to things, you could make a chicken speak like a man" (3.2.34). In other words, you'd have Foghorn Leghorn.
Seriously, though, this whole nommo, muntu, kintu stuff permeates through the entire book. How many times does Nathan Price get words wrong? How do some of the daughters' nicknames (like Rachel being called mvula, or termite) affect them? Sticks and stones may break our bones, but words... words have real power too.