perturbation in WordNet English dictionary

1. the act of causing disorder
   disruption  perturbation 
   
2. activity that is a malfunction, intrusion, or interruption
   "the term `distress' connotes some degree of perturbation and emotional upset"; "he looked around for the source of the disturbance"; "there was a disturbance of neural function"
   perturbation  disturbance 
   
3. an unhappy and worried mental state
   "there was too much anger and disturbance"; "she didn't realize the upset she caused me"
   disturbance  perturbation  upset 
   
4. a disposition that is confused or nervous and upset
   perturbation  fluster 
   
5. (physics) a secondary influence on a system that causes it to deviate slightly
   perturbation