milestone

US /ˈmaɪl.stoʊn/
UK /ˈmaɪl.stoʊn/
"milestone" picture
1.

an important stage or event in the development of something

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The discovery of penicillin was a major milestone in medicine.
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Graduating from college was a huge milestone for her.
:
landmarkturning pointwatershedbreakthroughachievement
2.

a stone set up beside a road to mark the distance in miles from a particular place

:
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We passed the ten-mile milestone on our journey.
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The old Roman milestones are still visible in some areas.
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markerwaymarkpost