the word 'thorny' is a straightforward english formation, combining the ancient germanic root for a sharp spike with a common adjectival suffix. its progenitor, the old english noun 'þorn', shares a common proto-germanic ancestor with words in other germanic languages, all denoting a sharp point, and can be traced back to the proto-indo-european root (s)ter- meaning "stiff, rigid". the literal meaning, "full of thorns," as in a rose stem, emerged naturally from this combination. the figurative sense, describing a difficult or contentious issue, evolved through metaphor, likening the pain and entanglement of a physical thorn to the challenges of a complex problem, a semantic shift that solidified by the 16th century.

Structure: thorn (sharp point on a plant) + y (adjective-forming suffix) thorn: from old english 'þorn', of germanic origin; related to dutch 'doorn' and german 'dorn'. functions as the core noun root meaning a sharp, stiff point on a plant. y: a native english suffix of old english origin, used to form adjectives from nouns, meaning "characterized by" or "full of".