Good question. The Kikongo word "nommo" means "name", but also it is the force that makes things live - a kind of soul or life force perhaps? A significant quote about "nommo" is:
Nommo comes from the mouth like water vapour: a song, a poem, a scream, a prayer, a name, all these are nommo. Water itself is "nommo", of the most important kind.
There do seem to be parallels with the idea of naming and Biblical ideas of the word ("In the beginning there was the word" etc). In the first part of the book, Genesis, quotes are made from the Biblical book of Genesis about naming the creatures and plants, and one of the themes of the book seems to be the linguistic relationship of words to each other in the Kikongo language as opposed to English. Consider this quote:
We worried over "nzolo"--it means "dearly beloved"; or a white grub used for fish bait; or a special fetish against dysentery; or little potatoes. ""Nzole" is the double-sized pagne that wraps around two people at once. Finally I see how these things are related. In a marriage ceremony, husband and wife stand tightly bound by their "nzole" and hold one another to be the most precious:"nzolani". As precious as the first potatoes of the season, small and sweet like Georgia peanuts. Precious as the fattest grubs turned up from the soil, which catch the largest fish. And the fetish most treasured by mothers, against dysentery, contains a particles of all the things invoked by the word "nzolo": you must dig and dry the grub and potatoes, bind them with a thread from your wedding cloth, and have them blessed in a fire by the nganga doctor.
Naming and the relationship of the names of words to each other represent another world to the characters within this book, only serving to highlight the cultural conflict that divides them and also perhaps reflecting on the poverty of our Western worldview that has such a different outlook.
"Nommo is the force that makes things live as what they are: man or tree or animal;" nommo means word (209). The Congolese are very spiritual people, and they believe that all things have spirits. All humankind are muntu, or man or people. There is no distinction between "living people, dead people, children not yet born, and gods" (209). All other things are kintu; "a place or a time is hantu;" and a "quality of being" is kuntu (209). This is because they all are being, from the stem ntu (209). Yet to be awakened from the ntu state, they need to be touched by nommo, existing (209). Nommo is significant because this defines who you are and what exists. Despite being identical twins, Leah is Leah because she is named Leah; Adah is Adah because she is named Adah. Names are important in defining a character.