IPA: /ˈpeɪn.ləs/
KK: /ˈpeɪnləs/
Not causing any discomfort or suffering; easy and without pain.
The dentist assured me that the procedure would be painless.
Painless → It is formed from "pain" (from Old French *peine*, meaning suffering or discomfort) and "-less" (meaning without). The word "painless" means without pain or free from suffering.
Think of being 'without' ('-less') 'suffering' ('pain') — that's why painless means free from pain.