IPA: /ˈsmaɪl.ləs/
KK: /ˈsmaɪl.ləs/
Not having a smile or appearing without a smile.
She looked smileless during the serious meeting.
Smileless → It is formed from "smile" (from Old English *smīlan*, meaning to smile) and "-less" (meaning without). The word "smileless" means without a smile or lacking a smile.
Think of someone who is 'without' ('-less') a 'smile' — that's why smileless means lacking a smile.