The Lowly Milestone

I was thinking about milestones today, how they used to be these hunks of rock to mark the distance in miles to a real place, but now there's no actual destination. We are not trying to get to Sydney, but instead marking an important event in history -- the first looping roller coaster, for instance, which appeared in 1840. Milestones made out of stone are rare, but milestones are everywhere and for always. Can you think of other words that have gone this route, from concrete to metaphor, fossilized words, as I think John Ciardi called them?