The word unreinforced implies something that is not strengthened or supported, and therefore it makes sense to consider antonyms that convey this notion of support or reinforcement. Antonyms for unreinforced could include words like fortified, reinforced, strengthened, supported, and buttressed. Alternatively, one could consider antonyms that suggest the presence of obstacles or weaknesses, such as fragile, unstable, vulnerable, weak, and feeble. Depending on the context in which the word unreinforced is used, different antonyms may be more appropriate. For example, if discussing a building's structure, reinforced may be the most appropriate antonym, while if discussing a person's mental state, vulnerable may be a better fit.