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Synonyms for Thorny (same or very similar meaning)

WordNet sense 1 (not easy; requiring great physical or mental effort to accomplish or comprehend or endure):
hard

WordNet sense 2 (having or covered with protective barbs or quills or spines or thorns or setae etc.):
barbed, barbellate, bristly, prickly, spiny, setaceous, briary, briery, bristled, burred, burry, setose

WordNet sense 3 ((used of plants and animals) furnished with bristles and thorns):
armed


From the ODE community, based on WordNetadd/edit