One who deprives of life; one who, or that which, kills.
- One that kills: a disease that was a killer of thousands; a killer of new ideas.
- Slang Something that is extremely difficult to deal with or withstand: an exam that was a real killer.
- Causing death or destruction: killer floods.
- Slang Having impressive or effective power or impact; formidable: had a killer smile; made killer profits.