Describing a super funny situation or occurrence. Often used by airheads or valley girls in cliques. Occasionally used by ghettofied bourgeoisie or people too lazy and dumb to pronounce the full word "hilarious".
"Hey Sher, like oh-emm-gee. That story was totally hilair, for sure."
My sister came up with this word to describe me when she was about eight years old. It is a portmanteau combining "hilarious" and "comedian." It is used sarcastically conveying the idea that "although you think you're funny, you're not."
Dude: Jack be not nimble; Jack be not quick; Jack couldn't jump over that there candlestick.
Bro: Hilarious, dude.
Dude: I'm a poet, I knows it.
Bro: Yeah, you're a real hilarian.