Massacre, slaughter, butchery, carnage, pogrom are comparable when they mean a great and often wanton killing of human beings.
Massacre implies promiscuous and wholesale slaying, especially of those who are not prepared to defend themselves and can make little or no resistance.
Slaughter, basically a butcher's term for the killing of animals used as food, suggests extensive and ruthless killing, whether the scene of that killing be a battle or a massacre.
Butchery adds to slaughter the implication of exceeding cruelty or of cold-blooded indifference to the sufferings of the victims.
Carnage is often not easily distinguishable from slaughter, except that it sometimes carries additional connotations similar to those of massacre.
Pogrom applies especially to an organized massacre of helpless people carried on usually with the connivance of officials. It is often applied specifically to such a massacre of Jews, especially in one of the European countries.