I came across this usage of "wicked" vs. "wickedly" when providing input to one of my knowledge group members. I had initially thought that for the following sentence, you need to use wickedly instead of wicked. Since sick is an adjective, we should use an adverb to modify an adjective. I was right about that grammar rule but wrong about the word “wicked”.
Wicked is normally used as an adjective; however, it can also be used as an adverb as a slang, meaning “extremely”, “really” or “totally”.
So for the following sentence, the meaning of the sentence will be completely different depending on which word you use.
This guy is wickedly sick.
= This guy is sinfully sick.
This guy is wicked sick. (Slang)
= This guy is extremely sick.
He is wicked cool.