adj. 25B6; adjective (informal) IMPERTURBABLE, unexcitable, cool, calm, {cool, calm, and collected}, self-controlled, cool-headed, level-headed; informal laid-back.
excitable.
UNFLAPPABLE
Meaning of UNFLAPPABLE in English
Concise Oxford thesaurus English vocabulary. Краткий оксфордский словарь английского языка тезаурус. 2012