infamousness comes from infamous + -ness, from Latin infamis ('of ill repute'), from in- ('not') + fama ('fame, report'), from fari ('to speak'). 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 notorious for something bad", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as infamous, infamy, fame, and famous. Its semantic neighborhood includes notoriety, infamy, disrepute, and ill-repute, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Latin infamis and Latin fama.