imperturbable

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The Word of the Day for August 3 is: 

imperturbable   \im-per-TER-buh-bul\   adjective
     : marked by extreme calm, impassivity, and steadiness : 
serene

Example sentence:
     As an emergency medical technician, Carol was expected to 
remain imperturbable even under the most chaotic and demanding 
of circumstances.

Did you know?
     There is an interesting time lag between the appearance 
of "imperturbable" and its antonym, "perturbable." 
Although "imperturbable" is known to have existed since the 
middle of the 15th century, "perturbable" didn't show up in 
written English until 1800. The verb "perturb" (meaning "to 
disquiet" or "to throw into confusion") predates 
both "imperturbable" and "perturbable"; it has been part of 
English since the 14th century. All three words derive from the 
Latin "perturbare," also meaning "to throw into confusion," 
which in turn comes from the combination of "per-" 
and "turbare," which means "to disturb." Other relatives 
of "imperturbable" include "disturb" and "turbid."