English

Noun

hair-trigger ‎(plural hair-triggers)

1. a trigger that will set off a firearm when even a very small pressure is applied
   • 1847: Francis Parkman, The Oregon Trail

     ... the hunter brings the sight of his rifle to bear; lightly and delicately his finger presses upon the hair-trigger.

   • 1872: Mark Twain, Roughing It

     Is your laugh hung on a hair-trigger?--that is, is it critical, or can you get it off easy?

Adjective

hair-trigger ‎(not comparable)

1. unstable, in a situation that could be worsened by the slightest mistake
2. easily angered, having a short temper
   • 1922, Peter B. Kyne, Cappy Rick Retires:

     "Gus," the latter began, "am I right in assuming that you possess a reasonable amount of influence with that hair-trigger partner of yours, Live Wire Luiz?"

   • 2014 October 21, Oliver Brown, “Oscar Pistorius jailed for five years – sport afforded no protection against his tragic fallibilities: Bladerunner's punishment for killing Reeva Steenkamp is but a frippery when set against the burden that her bereft parents, June and Barry, must carry [print version: No room for sentimentality in this tragedy, 13 September 2014, p. S22]”, in The Daily Telegraph (Sport):

     [I]n the 575 days since [Oscar] Pistorius shot dead his girlfriend Reeva Steenkamp, there has been an unseemly scramble to construct revisionist histories, to identify evidence beneath that placid exterior of a pugnacious, hair-trigger personality.