treacherous

Full of knots; knotty; twisted; crossgrained.

full of knots or gnarls Mississippi: Early Logging

used of old persons or old trees; covered with knobs or knots; "gnarled and knotted hands"; "a knobbed stick"

Used to describe hard or difficult climbs or moves

That which is fun, scary, difficult and abusive all in one. "That was one gnarly bit of single track."

any rough or treasonous thing.

Generally means intimidating. Usually when the waves are really powerful or there are rocks in places you wouldn't want them

large, 3 dimensional