This console command will set your target's health to 0, killing them. Essential characters cannot be killed. To kill your own character, use 'player.kill'
kill [reference id] Target Command
|Reference ID||This argument is optional. The reference ID of NPC you wish to be the murderer. If you don't specify anything here (recommended), there will be no killer.|
The above command would set your character's health to 0, killing you.
This cheat would set the health of your target to 0, killing them. Note that if your target is an essential NPC (an NPC that's required for things like quests, etc), it will not die.
This command WOULD NOT kill the NPC with reference ID 0078783. This command would kill the NPC you currently have selected as a target and declare the NPC with reference ID 0078783 as the killer.