The word "ultra-sensitive" denotes a high degree of sensitivity or reactivity, often to small changes or stimuli. Some synonyms for this term could include hyper-sensitive, highly reactive, delicate, vulnerable, or tender. Other possibilities might include touchy, irritable, easily agitated, or finely attuned. Depending on the context and the level of emphasis needed, similar words such as oversensitive, thin-skinned, delicate, or even fragile might also apply. Whether describing a person who is easily offended or a system that requires careful handling, these synonyms help to convey a nuanced understanding of sensitivity and its effects.