An important event in a person's life or career, in the history of a nation, in the life of some project, etc.
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.
To plan out a project as a series of major steps.
To place milestones along (a road, etc.).
A disaster, especially one which is large in scale and readily seen by public observers.
The aftermath of a train crash.
Someone (especially a woman) who is unbalanced and considered a mess, a disaster, one who is suffering personal ruin.
To ruin utterly and catastrophically, to cause to end in disaster.