According to Modernism, what is an "antihero"?

I'm writing a thesis paper on The Great Gatsby, and i'm trying hard to come up with a thesis... it has to be something about what the author is saying/doing/why... and how using modernist techniques helps prove why my thesis is true... i'm trying to play around with the idea that nick might be an antihero, as in someone who plays the role of a hero, but does not aid in solving conflicts that happen, because in the story nick was never really involved with the characters' lives, he just watched events take place... so this ties in with the theme of isolation... but that might be absolutely wrong... please help me? ):