"Manyness" is a term that refers to the quality or state of being many or numerous. Despite not having widely known synonyms, a few alternatives exist to convey a similar meaning. "Abundance" signifies a large quantity or plentifulness, while "copiousness" relates to the state of being ample or abundant. Another synonym to consider is "multitude", which refers to a great number or a large crowd. Similarly, "plenty" evokes the concept of a substantial amount or an abundant supply. While these synonyms might not be perfect substitutes for "manyness", they can help express the idea of a large quantity or numerousness in various contexts.