I’m not clear, did you not find hip in a dictionary, Dale? The OED2 gives it as equivalent to hep:

Hep, (a)
slang (orig. U.S.).
Well-informed, knowledgeable, ‘wise to’, up-to-date; smart, stylish. Hence as n., the state of being ‘hep’. Also as v., to pep up; hepped ppl. a. (often with up); to be hepped on, to be enthusiastic about, ‘bitten with’. Cf. hep-cat, hip a.

1908 Sat. Even. Post 5 Dec. 17/1 What puzzles me is how you can find anybody left in the world who isn't hep. 1914 Jackson & Hellyer Vocab. Criminal Slang 43 Hep,+. Sapiency; understanding.+ Derived from the name of a fabulous detective who operated in Cincinnati.

© Oxford University Press