The adverb 'startlingly' is built upon the verb 'startle', which itself emerged in Middle English as a frequentative form of the verb 'start', meaning to cause someone to make a sudden, quick movement out of surprise or fear. The core concept originates from the Old English styrtan, meaning "to leap up" or "to jump," a vivid physical action. By adding the '-ing' suffix, the verb becomes the adjective 'startling', describing something that causes such a reaction. Finally, the adverbial suffix '-ly' transforms it into 'startlingly', a word that describes the manner in which something is surprising or shocking, thus completing the evolution from a literal, physical leap to a modern descriptor of abstract, mental astonishment.

Structure: startle (to alarm) + ing (adjective suffix) + ly (adverb suffix) - startle: From Middle English stertlen, a frequentative verb from sterten (to leap, rush). Its ultimate origin is Old English styrtan (to leap up, start), of Germanic origin. - ing: A suffix of Germanic origin used to form present participles and adjectives from verbs. - ly: A suffix of Germanic origin (Old English -līce) used to form adverbs from adjectives.