Imperturbability means being calm and composed, even in difficult or stressful situations. It refers to someone who maintains their inner peace and doesn't easily get agitated or disrupted by external events. Full definition
Best Direction: An equitable nod toward both the passionate imperturbability of Luis Buñuel, That Obscure Object of Desire, and the vaulting enthusiasm of Ridley Scott, The Duellists. (parallax-view.org)
In its double structure — at once syntagmatic and paradigmatic — Quint's reading of the poem mirrors the truth that was taught us by Geoffrey Hartman in his seminal essay «Milton's Counterplot» (1958): Beneath and above the superficial and superficially attractive busyness of the verse's narrative propulsion is the «divine imperturbability,» the «calm and cold radiance» that reigns always at the poem's still center. (firstthings.com)
The task was to still the restless activity of the mind so that the true self could become visible in its absolute imperturbability. (religion-online.org)