Gnarly (adjective)

1. Extremely difficult or dangerous.
2. Awesome, excellent.

Origin:

Surfing slang from the 1960s.

Examples:

1. The wave was gnarly and only experienced surfers should attempt to ride it.
2. He was gnarly in the halfpipe competition, landing difficult tricks with ease.
3. That was a gnarly trick you pulled off.
4. That math problem was gnarly, I couldn't solve it.
5. Gnarly dude, you really nailed that performance.