milestone/ˈmaɪlˌstoʊn/EtymologyFrom mile + stone. Compare Dutch mijlsteen (“milestone”), German Low German Mielensteen (“milestone”), German Meilenstein (“milestone”), Swedish milsten (“milestone”).milestone 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. Lexicurio rates it Rare gem — a strength score of 70 out of 100.nounA 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.An important event in a person's life or career, in the history of a nation, in the life of some project, etc.“Death is another milestone on their way.”verbTo place milestones along (a road, etc.).To plan out a project as a series of major steps.