self-possession
1. [ noun ] the trait of resolutely controlling your own behavior
Synonyms: self-will willpower possession self-command self-control
Related terms: resoluteness nerves presence_of_mind
2. [ noun ] great coolness and composure under strain
Synonyms: aplomb poise cool sang-froid assuredness
Examples:

"keep your cool"

Related terms: composure brace
Similar spelling:   self-possessed
  self-expression
  self-assertion
  self-suggestion