IPA: /ˈpeɪn.ləs.nəs/
KK: /ˈpeɪnləsnəs/
The state or quality of not causing any pain or discomfort.
The doctor assured her that the procedure would be done with complete painlessness.
Painlessness → It is formed from "pain" (from Old French *peine*, meaning suffering or discomfort) and "-less" (meaning without) and "-ness" (meaning a state or condition). The word "painlessness" refers to the state of being without pain or discomfort.
Think of being 'without' ('-less') 'suffering' ('pain') — that's why painlessness means the state of having no pain.