So there's this fantasy creature, right? Turns out the word "lich" isn't a random one, but instead it's a real (albeit outdated) English word for "corpse/dead body". A bunch of Germanic languages have cognates, for example Norwegian "lik" (corpse) and German "Leiche" (also "corpse").
Interestingly, the suffixes -ly/-like (as in, "childlike" and "manly") are also related to this word!
From *līką (Proto-Germanic word for "body" in both alive and dead senses), originally with the sense of 'having the body or form of'.