Word of the day · today
Milestone
UK /ˈmaɪlstəʊn/US /ˈmaɪlˌstoʊn/
The Romans set stones along their roads every thousand paces, a mille passus, and a mile is still, roughly, a thousand Roman paces. Britain revived the practice in the eighteenth century, when the turnpike trusts were required by law to mark their roads, and the surviving stones are listed monuments. A milestone was a point you passed, and by the nineteenth century it was a point you reached in a life or a project.
Project managers and investors use it constantly and rarely think of the stone. A milestone payment is money released when a stage is finished, and the metaphor still works: you cannot move the stone once you have set it.