Keep One's Cool Meaning

(idiomatic) To remain composed, calm, and even-tempered, especially in a provocative situation.

Example: 1990, Michael Martinez, "THE PLAYOFFS: By the Way, Stewart Leads A's Into Series," New York Times, 11 Oct. (retrieved 3 June 2009):
  In the heat of the afternoon, while Roger Clemens threw a temper tantrum and the Boston Red Sox became unraveled, Dave Stewart kept his cool.
2009, Kevin Purdy and Lukas Alpert, "‘The Next Thing I Knew the Ceiling Was on Me’," New York Post, 4 June (retrieved 3 June 2009):
  Fighting back panic, she tried to keep her cool and find a way out from under the rubble.