'Milestone' definitions:

Definition of 'milestone'

From: WordNet
noun
Stone post at side of a road to show distances [syn: milestone, milepost]
noun
A significant event in your life (or in a project)

Definition of 'Milestone'

From: GCIDE
  • Milestone \Mile"stone`\, n.
  • 1. A stone serving the same purpose as a milepost. [1913 Webster]
  • 2. An event or accomplishment marking a significant advance in an endeavor; a notable achievment; as, putting a man in orbit was a major milestone on the way to the moon.
  • Syn: milepost. [PJC]

Synonyms of 'milestone'

From: Moby Thesaurus