relaxing in a calm way, or making someone feel frightened or nervous; causing a feeling of cold.
From Old English 'ciele' meaning 'cold'. As a verb, it means to make cold, but in modern slang 'chilling' means relaxing, and as an adjective it can mean frightening or cold.
The word 'chilling' has split into two completely opposite meanings—relaxing with friends versus being creepy and scary—and context is everything! It's a great example of how slang completely rewires old words.
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