One meaning, the one that I've always known and thought about it when someone said the word "chill", was "very relaxed or easy going" with the example "in general, I am a pretty chill guy", as given by the definition when you search the word on Google.
However, another definition is "an unpleasant feeling" or even to "horrify or frighten someone", with the example "there was a chill in the air".
Even though the word chill in the first example is informal, still I find the 2 definitions in contrast with each other — opposite.
My question is why do we have today this word with two completely different meanings? When did the informal meaning appear? Does it cause some confusion?