Definition of "gnarly"

Out of one window I can see the garden, those mysterious deep-shaded arbors, the riotous old-fashioned flowers, and bushes and gnarly trees.

1892 January, Charlotte Perkins Gilman, The Yellow Wall Paper, Boston, Mass.: Small, Maynard & Company, published 1901, page 13

There ain't nothing gnarlier (apparently) than slapping on some brightly coloured sunblock to ward off the blinding spectre of dangerous, snow-reflected sunlight.

2000 January 16, Sunday Herald, Glasgow

When the swell struck, the North Shore got gnarly, and the wise ones hit the outer islands where the energy was just as juicy but a bit more organized.

1977 March, Surfer

Work that makes you unhappy is what I mean by "a gnarly problem." The trouble is, the market pays for solutions to gnarly problems, not solutions to easy problems. As the Yorkshire lads say, "Where there's muck, there's brass."

2008, [Avram] Joel Spolsky, More Joel on Software: Further Thoughts on Diverse and Occasionally Related Matters that will Prove of Interest to Software Developers, Designers, and Managers, and to Those who, whether by Good Fortune or Ill Luck, Work with Them in Some Capacity, Berkeley, Calif.: Apress, page 152

We're not talking about a lame chick and a gnarly guy. We're talking about a couple of far-out dudes.

1981, Dan Jenkins, Baja Oklahoma, New York, N.Y.: Atheneum Books, ISBN 978-0-689-11173-0; reprinted New York, N.Y.: Pocket Books, 1982, ISBN 978-0-671-45163-9, page 269

Funky Kong: 'Those Snowmads are a gnarly bunch! I hear they're enjoyin' your island. Go get 'em, DK!'

2014 February, Retro Studios, Donkey Kong Country: Tropical Freeze, Nintendo, level/area: Funky's Fly 'n' Buy