Excitability is the quality of becoming excited too easily — how quickly a person, an animal, or even a nerve in the body jumps to a strong feeling or a strong reaction. If a child has high excitability, a small surprise can make them shout, laugh, or get upset. In everyday talk it often describes personality, and it can sound a little critical, as if the person cannot stay steady. Though actually, doctors and scientists also use it in a cooler way: the excitability of a muscle or a nerve means how readily it fires. The related adjective is excitable. It names a tendency, not one burst of excitement.

易興奮、興奮性（可指個性，也可指神經或肌肉）