heinousness comes from heinous plus the noun-forming suffix -ness; heinous derives from Old French haineus, hainos ('hateful'), from haine ('hatred'), from hair ('to hate'), of Frankish (Germanic) origin. 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 utterly wicked or atrocious", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as heinous and heinously. Its semantic neighborhood includes atrocity, wickedness, monstrousness, and enormity, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Old French haineus and Proto-Germanic *hatjan.