Since the fall I’ve heard the word “epic” used in a novel way that would qualify as slang. Rather than the two thousand year old “epic poem” or “epic tale,” it’s still an adjective but used in place of “awesome” or “incredible.” For example:
It was an epic road trip.
An epic night with my friends.
I’d say it’s a slang use of the word, although it’s not far from its original meaning. Here’s its adjectival definition:
of, relating to, or characteristic of an epic or epics
heroic or grand in scale or character
The recent use follows the second definition.
Here’s one Urban Dictionary’s many definitions for it:
Awesome, kickass, or otherwise positive. Can be used to refer to anything but is usually referring to a particular event or action. The most common usages are "epic win" or "epic failure," and some prefer to type it in all caps. Occasionally people use the phrase "Epic ___" as a stand-alone sentence or phrase, always following a story about something considered Epic.
"Epic Movie" came out in 2007. This may have something to do with its popularity, even the movie itself wasn't popular.
Before the last year, the word “proportions” usually followed it, but now it’s all on its own and doing fine.