harshly comes from harsh plus the adverbial suffix -ly; harsh derives from Middle English harsk ('rough, sour'), of Scandinavian origin, akin to Old Norse hǫrskr. 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 adverb sense is "in a severe, rough, or unkind manner", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as harsh and harshness. Its semantic neighborhood includes severely, sternly, roughly, and brutally, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Middle English harsk.