pain·kill·er 
(pānkĭl′ər)
(pānkĭl′ər)n.
An agent, such as an analgesic drug, that relieves pain.
painkill′ing adj.
- opportunism
- opportunist
- opportunistic
- opportunistic infection
- opportunity
- opposability
- opposable
- oppose
- opposer
- opposite
- opposite field
- opposite-field
- oppositely
- oppositeness
- opposite number
- opposition
- oppositional
- oppositionist
- oppress
- oppression
- oppressive
- oppressively
- oppressiveness
- oppressor
- opprobrious