imaginativeness comes from imaginative + -ness, from Latin imaginari ('to picture to oneself'), from imago ('image, likeness'). Morphologically, the ending is part of the etymology: the suffix is attached to the older base named in the history, producing a later English derivative. In present English, the noun sense is "the quality of being creative and inventive", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as imagine, imaginative, and imagination. Its semantic neighborhood includes creativity, inventiveness, ingenuity, and originality, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Latin imaginari and Latin imago.