milestone

Etymology

mile + stone.

noun

1. 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.
2. (idiomatic) 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. 1933, Stephen Spender, The Funeral
   Creating a complete map of the human connectome would therefore be a monumental milestone but not the end of the journey to understanding how our brains work. 2012 March-April, Terrence J. Sejnowski, “Well-connected Brains”, in American Scientist, volume 100, number 2, archived from the original on 2017-04-27, page 171
   She bought the model as a surprise gift for a friend who is a lifelong HST fan and railwayman, and who will soon be celebrating a milestone birthday. October 20 2021, “Stop & Examine”, in RAIL, number 942, page 71

verb

1. To place milestones along (a road, etc.).
2. (idiomatic) To plan out a project as a series of major steps.