This book is about meaningness. “Meaningness” is a word I invented, referring to the quality of being meaningful and/or meaningless.
The word “meaning” has two quite different meanings in English. It can refer to the meaning of symbols, such as words and road signs. This book is not about that kind of meaning.
People also speak of “the meaning of life.” That is the sort of meaningness this book is about. So I apply “meaningness” only to the sorts of things one could describe as “deeply meaningful” or “pretty meaningless.” The book is about matters such as purpose, ethics, and selfhood.
Meaningness is a quality, not a thing. I don’t think there is a definite meaning of life. Meaningness is always nebulous: indefinite, uncertain, ambiguous.
The suffix -ness constantly reminds one of this nebulosity. I mostly avoid the word “meaning,” because it builds in the assumption that something meaningful has one specific meaning. Often, that is wrong.