Complex sentence: The origins of the terms "hip" and "hep" are uncertain, although by the 1940s both had become part of African American jive slang and meant "sophisticated; currently fashionable; fully up-to-date".
Split into simpler sentences: The origins of the terms "hip" and "hep" are uncertain. Although, by the 1940s, both had become part of African American jive slang and meant "sophisticated; currently fashionable; fully up-to-date".