Unshakably calm and collected. See Synonyms at cool.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "imperturbable" in a sentence
"Osman can scarcely be called imperturbable, for he has his daily and hourly moods, and is of varying temper; but he carries himself always as though conscious of being an outcast, whom nothing can either elevate or defile."
"And the other, calm-eyed, cool-browed, serene; strong in her own integrity, with faith in herself, thoroughly at ease; dispassionate, imperturbable; a figure chiselled from some cold marble quarry."
"He turned on his moccasined heel and walked out, imperturbable, sphinx-like, neither giving nor receiving greetings nor looking to right or left."