The story
From mile + stone. Compare Dutch mijlsteen (“milestone”), German Low German Mielensteen (“milestone”), German Meilenstein (“milestone”), Swedish milsten (“milestone”).
Etymology from Wiktionary, CC BY-SA 4.0.
milestone
Today it means: A stone milepost (or by extension in other materials), one of a series of numbered markers placed along a road at regular intervals, typically at the side of the road or in a median. Full definition →