Word Distinction: Killing

Kill is a general word meaning to cause (anything or anybody) to die.
My uncle was killed in a plane crash.
The cold weather killed our tomato plants.

Murder means to kill a person on purpose.
She was sent to prison for murdering her husband.

Slaughter and butcher mean to kill animals for food, but both words are also used to describe cruel or unnessary killing of humans.
Our army was butchered by the enemy's much larger forces.
Thousands of people are needlessly slaughtered in road accidents.

To assassinate means to kill an important political figure.
an attempt to assassinate the president

To massacre means to kill large numbers of (defenceless) people.
The army entered the city and massacred all the women and children.