Mine is “palimpsest”. I first encountered this word while reading The Secret History by Donna Tartt.
Definition: a manuscript or piece of writing material on which the original writing has been effaced to make room for later writing but of which traces remain.
I love that there’s a word for this.
I discovered ‘jeroboam’ in The Difference Engine by Gibson & Sterling. It’s an interesting word: when capitalized, it’s a Biblical king; otherwise, it’s a bottle.