IPA: //ˈpeɪnˌkɪlər//
KK: /ˈpeɪnˌkɪlər/
A substance that helps to reduce or eliminate pain in the body.
After the surgery, the doctor prescribed a painkiller to help manage the discomfort.
Painkiller → It is formed from "pain" (from Old French *peine*, meaning suffering or discomfort) and "killer" (from Old English *cyning*, meaning to cause death or to end). The word "painkiller" refers to something that ends or alleviates suffering or discomfort.
Think of something that 'ends' ('killer') your 'suffering' ('pain') — that's what a painkiller does.
No commonly confused words.