Definition from Wiktionary, the free dictionary
- Remaining composed and level-headed at all times; unswayed by adversity or excitement; impossible to fluster; not becoming frustrated or irritated easily. [1954 to date]
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
- (remaining composed under pressure): flappable