Green’s Dictionary of Slang

hip n.2

also hipness
[hip adj. (1)]

1. (orig. US black) sophistication, the prevailing fashion.

[US]Kerouac letter 2 Jan. in Charters I (1995) 141: I heard some of the cats discussing him in the john – cats with beards and artistic-looking manners and real Bohemian hipness, etc.
[US]Kerouac letter 11 Feb. in Charters II (1999) 114: He has great vocal ability to explain beatness and hipness.
[US] in S. Harris Hellhole 126: Cora May admits [...] that her own ‘hipness’ and ‘downness’ didn’t get her far.
[Aus]B. Oakley Salute to the Great McCarthy 157: An apparition all of a sudden at the oor. ‘Albert! Albert the hip!’.
[UK]Guardian Guide 3 July–9 July 89: Massive Attack have managed to remain the epitome of hip.
[UK]Indep. Rev. 21 Jan. 14: A calculated avoidance of the mainstream, a deliberate rejection of potentially damaging hipness.

2. a sophisticate, in the context of the beat/drug subculture.

[US]L. Block Diet of Treacle (2008) 49: Squares could turn Hip if they were sick enough, but Hips like you [...] couldn’t return to Squaresville.
C. Sellers Where Have All the Soldiers Gone 114: All the hips weren’t like Cat Yates. There were people who’d give away anything they had.

In derivatives

hipdom (n.)

the world of subcultural sophistication.

[US]L. Block Diet of Treacle (2008) 107: Not sick enough to throw herself headlong into the hysteria of hipdom.
[US]Buerkle & Barker Bourbon Street Black 199: [T]he jazzman is usually seen to be in desperate combat with conventional society. Possessed by his music, this ‘outsider’ is seen to retreat to small enclaves of ‘hipdom’ to avoid the ‘squares.’.