late Middle English : from late Latin imperturbabilis , from in- not + perturbare (see perturb )
Adjective
Similar Words: self-possessed composed collected calm cool, calm, and collected as cool as a cucumber cool-headed self-controlled poised tranquil serene relaxed easy-going unexcitable even-tempered placid sedate phlegmatic unperturbed unflustered untroubled unbothered unruffled undismayed unagitated undisturbed unmoved nonchalant at ease unflappable unfazed together laid-back nonplussed equanimous
Opposites: edgy excitable