Murderer = Someone who takes a life Killer = Same as murderer Assassin = Is a profession where an individual kills people through contracts and eliminates the people its employer desires to be killed. Slayer = This word generally means a murderer but is used to describe murderer's who are known to be extremely violent. If someone is slain they have been killed very violently.

killer-Someone who causes the death of a person or animal Murderer-A criminal who commits homicide (who performs the unlawful premeditated killing of another human being) Assasin-A murderer (especially one who kills a prominent political figure) who kills by a surprise attack and often is hired to do the deed slayer-same with killer cowboy...

Hi, why not type your words into www.thefreedictionary.com and you will get your answers.

it is simple... they all kill

There is no difference, all of them mean this word = death