40s cool

In his book Jazz: A History (1977), Frank Tirro defines the 1940s hipster:

To the hipster, Bird was a living justification of their philosophy. The hipster is an underground man. He is to the Second World War what the dadaist was to the first. He is amoral, anarchistic, gentle, and overcivilized to the point of decadence. He is always ten steps ahead of the game because of his awareness, an example of which might be meeting a girl and rejecting her, because he knows they will date, hold hands, kiss, neck, pet, fornicate, perhaps marry, divorce—so why start the whole thing? He knows the hypocrisy of bureaucracy, the hatred implicit in religions—so what values are left for him?—except to go through life avoiding pain, keep his emotions in check, and after that, "be cool," and look for kicks. He is looking for something that transcends all this bullshit and finds it in jazz.

Marty Jezer, in The Dark Ages: Life in the United States 1945–1960 (1999), provides another definition:

The hipster world that Kerouac and Ginsberg drifted in and out of from the mid-1940s to the early-1950s was an amorphous movement without ideology, more a pose than an attitude; a way of "being" without attempting to explain why. Hipsters themselves were not about to supply explanations. Their language, limited as it was, was sufficiently obscure to defy translation into everyday speech. Their rejection of the commonplace was so complete that they could barely acknowledge reality. The measure of their withdrawal was their distrust of language. A word like cool could mean any of a number of contradictory things—its definition came not from the meaning of the word but from the emotion behind it and the accompanying non-verbal facial or body expressions. When hipsters did put together a coherent sentence, it was always prefaced with the word like as if to state at the onset that what would follow was probably an illusion. There was neither a future nor a past, only a present that existed on the existential wings of sound. A Charlie Parker bebop solo—that was the truth.