The brilliant tenor-saxophone player Lester Young was a fabulous wordslinger. He hung the name “Sweets” on candy-loving trumpeter Harry Edison, pinned rotund jazz singer Jimmy Rushing with “Mr. Five-by-Five,” and dubbed Billie Holiday (whom Duke Ellington pronounced “the essence of cool”) “Lady Day.” In the documentary Song of the Spirit, a Young biographer, Douglas H. Daniels, claims that Young coined the phrase “that’s cool.” Jackie McLean, the great bop alto player, agrees: “Anyone who tells you otherwise is bullshitting,” he warned me. “Lester Young was the first.”

An intensely private, solitary man, so cool he wore crepe-soled shoes, Young’s Fu Manchu mustache and trademark porkpie hat were pieces of a mask that hid many things. To most of the world, Young appeared unruffled and fastidious. He always came in a moment after the beat, just to remind you that you were on Lester’s time. Even when he was sitting in the window of his final room, across the street from Birdland at the Alvin Hotel, knocking down his daily quart of hundred-proof, cool remained Lester Young’s unassailable castle, his signature.

Anybody trying to define “cool” quickly comes up against cool’s quicksilver nature. As soon as anything is cool, its cool starts to vaporize. To Carnegie Mellon emotionologist Peter Stearns, cool symbolizes “our culture’s increased striving for restraint” to better blend into the social fabric. In his American Cool: Constructing a Twentieth-Century Emotional Style, Stearns says to be cool means “conveying an air of disengagement, of nonchalance, and using the word is part of the process of creating the right impression.” We can “lose” or “blow” our cool, Stearns points out. Cool, he goes on, “has become an emotional mantle, sheltering the whole personality from embarrassing excess.”

In her book What Is Cool?: Understanding Black Manhood in America, Marlene Kim Connor says, “Cool is perhaps the most important force in the life of a black man in America [italics Connor’s]. Cool is the closest thing to a religion for him, and it is easily his most basic method of determining manhood. Cool cannot be taught, or handed down from generation to generation.” For black men, “Cool essentially defines manhood.” Only one’s peers can bestow cool.

“Cool for us, was to be there without being into nothing dumb,” the poet Amiri Baraka writes in his Autobiography. In Newark, New Jersey, “where I was comin from, the brown side, we just wanted to keep steppin. The black had shaped us, the yellow had taunted us, the white had terrified and alienated us. And cool meant, to us, to be silent in the face of all that, silent yet knowing.” Later, cool meant well dressed: “dap,” “clean,” “down,” “hooked up.” To Baraka, just being from New York was cool. The coolest guy in his Howard University set was “Smitty from the city.” Bop was cool. The original Birth of the Cool 78s came out when Baraka was a senior in high school. “For me, Miles was what cool meant.”

Clarence Majors traces cool back to the first rebellious slave submerging his emotions in irony and choking back his rage. “Black cool,” adds Dr. Richard Majors, a psychologist and senior research associate at the Urban Institute in Washington, “is better understood as a complex system of coping mechanisms, a technique for black survival in America.” “I play it cool,” Langston Hughes wrote, “And dig all jive/That’s the reason/I stay alive.”

Marlene Kim Connor posits that cool arose when male slaves were forced to maintain an outward calm while their wives and mothers and daughters were raped by white men. For an African-American male, “being cool” meant that he had harnessed his anger. Indeed, as Connor writes, “A man’s ability to protect himself is at the very core of cool.” Cool, then, became the ultimate revenge of the powerless. Cool was the one thing that the white slaveowner couldn’t own. Cool was the one thing money couldn’t buy. At its core, cool is about defiance.

For a white hipster like Garry Goodrow, an actor in New York’s Living Theater throughout most of the 1950s, “to be cool was to be in charge, unfazed by the bullshit of life .... The outward signs of cool had everything to do with an appearance of easy competence .... To be cool was to be not frantic, not overblown.” In Goodrow’s world, black people had the keys to cool, “to many beautiful, life-affirming things—like jazz, like relaxation, like general enjoyment of life outside the commercial pressure cooker. Any white who felt a healthy disgust for the ridiculous society around him gravitated in that direction.”

The poet and critic Peter Schjeldahl sees cool as transcending race, citing the unemployed aristocracy disenfranchised by the French Revolution as one likely source of the cool. “Cool is one of the consolations for the aristocracy’s loss of power—[cool is] an inborn excellence that you don’t have to prove.”