In Reply to: Lose one's cool posted by John Reuter on September 29, 2009 at 06:17:
: Does anyone know the origin of "to lose one's cool"?
The Oxford English Dictionary cites an example from the early 1960s (and many thereafter):
OED, s.v. cool "b. slang (orig. U.S.). Composure, relaxedness; poise, self-control. Esp. in to keep (also blow, lose) one's cool.
[Examples:1964 Times Rec. (Troy, N.Y.) 28 Feb. 21/2 Sonny just went to pieces. He lost his cool. . . ."
This use of cool seems to go back to the "cool jazz" of the 1940s, and specifically to the 1949 album of cool jazz by Miles Davis, cited by the OED as "[1949 M. DAVIS et al. (title of album) Birth of the Cool.]" Davis was no doubt pointing to the contrast between his kind of jazz and "hot jazz."
Cool as an adjective has long been used figuratively to mean calm, composed, detached or dispassionate. After World War II, if not sooner, the adjective started to be used as a noun.