sick, adj. and n.

c. In phrases sick as a dog, horse, etc. ( Sense sometimes merging with 4). Also sick as a parrot (a fanciful catch-phrase, chiefly used joc.).

1982 Daily Star 5 Feb. 5/6 Peter the budgie was sick as a parrot until a vet diagnosed his problem yesterday. Peter..has got gout!

slang (now esp. Skateboarding and Surfing). Excellent, impressive; risky.

1983 UNC-CH Campus Slang(Univ. N. Carolina, Chapel Hill) (typescript) Spring 5 Sick, unbelievably good: The Fleetwood Mac concert was sick. 1992 Caribbean Week Apr. 26/1 ‘A really sick car’ is an attractive, eye-catching vehicle and not one that's ready for the repair shop. 1997 BMX Plus! Apr. 56 (caption) Jeff Harrington has some of the sickest jumping variations we have ever seen. 2002 U.S. News & World Rep. 21 Jan.-4 Feb. 63/1 ‘That's siiiick!’ gushes an admiring fan.