1. The quality of being readily enthusiastic or feeling eager to do something: Byron noticed the excitability of his dog when he was about to take it out for a walk.
2. The reactions manifested by living organisms, and the elements and tissues of which they are constituted, by responding to the actions of stimulants: Dr. Wolf told Etta that she had a nervous excitability that was being influenced by the physical, chemical, and electrical forces in her body.