Skittishness is a quality of being anxious and fidgety. Your cat's skittishness might send him racing to hide in the basement whenever your friends come to visit.
An airplane passenger's skittishness might draw the attention of airport security, while your own skittishness on the first day of school will hardly be noticed, since many students are a little nervous. The adjective skittish came first, and its original meaning was "very lively or frivolous," from a Scandinavian root. Later, it came to mean "shy or nervous," and frequently described jittery horses.