The contrasting meanings of the word "chill"

The original sense was used figuratively from the 19th century:

Chill:

Figurative sense "depressing situation or influence" is from 1821 (in Middle English the figurative sense was "suffering, misfortune").

(Etymonline)

The contemporary sense of relaxed is an AmE usage from the verbal expression “chill out:”

Chill out:

The idiom chill out means to relax or calm down. This idiom is commonly used in American English.

Chill out became popular in America in the 1970s and functions as a phrasal verb. However, unlike many phrasal verbs, this phrase may be shortened to chill while retaining its idiomatic meaning.

(writingexplained.org)

Chill:

(orig. US black) 1983 : calm, untroubled, relaxed.

(Green’s Dictionary of Slang)