The adverb 'stupidly' is formed by appending the ubiquitous English adverbial suffix '-ly' to the adjective 'stupid'. The core adjective originates from the Latin stupidus, meaning "struck senseless, stunned, or foolish," which itself derives from the verb stupere, "to be stunned or amazed." This verb is traced back to the Proto-Indo-European root (s)teu-, related to the concept of being pushed, struck, or stunned. Thus, the literal sense of being physically struck into a daze evolved metaphorically into the modern abstract meaning of lacking intelligence or acting in a foolish manner, with '-ly' specifying that an action is performed in such a way.

Structure: stupid (foolish) + ly (adverb suffix) - stupid: From Latin stupidus (struck senseless, amazed, foolish). Functions as the adjectival root. - ly: From Old English -līce (forming adverbs from adjectives). Functions as a derivational suffix indicating manner.