The word 'startling' is built upon the core action of a sudden, involuntary movement. Its root, 'startle', evolved from Middle English 'stertlen', which itself was an intensified form of 'sterten', meaning to leap or jump. This Germanic root conveys a primal sense of being physically jolted. The addition of the '-ing' suffix transforms this verb of action into an adjective describing the quality that causes such a reaction. Thus, the modern abstract meaning of 'very surprising or alarming' directly retains the logic of its literal origin: something so shocking it makes one jump.

Structure: startl (to move suddenly) + ing (adjective-forming suffix) 'startl' originates from the Middle English verb 'stertlen', a frequentative form of 'sterten' (to leap, to move suddenly), of Germanic origin. The '-ing' suffix is from Old English '-ende', a present participle ending used to form adjectives.