The word is German in its origins
But has been showing up in British culture
Since 1932, or thereabouts
In this context at least: the supernatural.
It comes from an archaic word for corpse:
Specifically a man, one of great power
Of royalty perhaps: no common peasant,
Who works dark magic, hoping to cheat death.
And thus, he becomes something half alive:
Handsome at first, in an unearthly way,
But as the years pass, the decay sets in
And he becomes cadaverous and gaunt.
Though he appears fragile, filled with rot,
The lich is said to wield unholy power
Controlling those who worship him and serve him
And forcing them to carry out his will.
There’s only one known way to kill a lich:
The creature has imbued his vital essence
Into a thing that he esteems as precious.
Destroy that, and you will destroy the monster.
(I did read, recently, somewhere or other
That someone had “destroyed the royal family”.
But that’s not really relevant, I’m sure.)