On page 138 of my edition of The Light Fantastic, Cohen the Barbarian tells Twoflower and Rincewind about trolls, and tries to say a word that I cannot at all identify (emphasis added):
"Trollsh never ate anybody."
"No, they alwaysh spit the bitsh out. Can't digesht people, see? Your average troll don't want any more out of life than a nice lump of granite, maybe, with perhapsh a nice slab of limeshtone for aftersh. I heard someone shay it's becosh they're a shilicashe—a shillycaysheou—" Cohen paused, and wiped his beard, "made out of rocks."
What could he possibly be saying? I had no idea; the best someone I asked could possibly think of was "Shillelagh", a word for a club that came from Irish. However, that really doesn't make much sense here.
What does this mean?