mile·stone /ˈmaɪ(ə)lˌston/
  里程碑,里程石,一里程標
  milestone
  里程碑
  milestone
  里程碑
  Mile·stone n.
  1. A stone serving the same purpose as a milepost.
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  milestone
       n 1: stone post at side of a road to show distances [syn: milepost]
       2: a significant event in your life (or in a project)