imperturbable
adjective
incapable of being upset or agitated; not easily excited; calm.
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
The door of Venner's slammed behind his imperturbableness, and a sigh of pent-up stupefaction was let loose.
From Sinister Street, vol. 2 by Compton MacKenzie