IPA: /ˈsʌn.ləs/
KK: /ˈsʌnləs/
Not having sunlight; dark and gloomy.
The garden looked sad and lifeless in the sunless winter days.
Sunless → It is formed from "sun" (from Old English *sunne*, meaning the star that provides light and warmth) and "-less" (meaning without). The word "sunless" means without sunlight or lacking the presence of the sun.
Think of being 'without' ('-less') the 'sun' — that's why sunless means lacking sunlight.