Nadir
I assume you are referring to the use of the term in relationship to goals and projects and not the original description of a stone marking off miles on a road. While it is not actually an antonym for a milestone, the opposite could be considered to be "setback".
Milestone Media ended in 1996.
Meeting at the Milestone was created in 1947.
Zero Milestone was created in 1923.
Milestone S.r.l. was created in 1996.
Milestone Records was created in 1966.
Milestone Systems was created in 1998.
Milestone Systems's population is 375.
Milestone Systems's population is 2,011.
Milestone Media was created in 1993.
Download Milestone 1.9 (Super Tux 0.3.3): If you have a Windows OS: