IPA: /ˈtʃɪl.nəs/
KK: /ˈtʃɪl.nəs/
The condition of being cold or cool in temperature.
The chillness in the air made everyone wear jackets.
Chillness is formed from "chill" (from Old English *ciele*, meaning cold) and "-ness" (meaning the state or quality of). The word "chillness" refers to the state of being cold or the quality of being chilly.
Think of the word 'chill' which means cold, and remember that 'chillness' describes the state of being cold.