unflappable

From un- +‎ flap (“to upset, stir”) +‎ -able.

• IPA^(key): /ʌnˈflæpəbəl/

• Audio (AU)

  (file)

unflappable (comparative more unflappable, superlative most unflappable)

1. Remaining composed and level-headed at all times; impossible to fluster; not becoming frustrated or irritated easily. [from 1954]

   Synonyms: collected, cool, even-keeled, imperturbable

   Antonym: flappable

   • 1959, The Economist, volume 190:

     The whole thing looked remarkably like an implacable force meeting an unflappable object.

   • 1978, James D. Margach, The abuse of power: the war between Downing Street and the media from Lloyd George to Callaghan:

     It was for this reason that when Lord Hailsham first described Harold Macmillan as "unflappable'", it became an instant catchword, distancing the incoming Prime Minister from his predecessor