imperially comes from imperial (from Latin imperialis, from imperium 'empire') + the adverbial suffix -ly. 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 manner befitting an emperor or empire; majestically", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as imperial, empire, and emperor. Its semantic neighborhood includes regally, majestically, royally, and grandly, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Latin imperialis and Latin imperium.