from
The Collaborative International Dictionary of English v.0.48
Landmark \Land"mark`\, n. [AS. landmearc. See {Land}, and {Mark}
a sign.]
1. A mark to designate the boundary of land; any mark or
fixed object (as a marked tree, a stone, a ditch, or a
heap of stones) by which the limits of a farm, a town, or
other portion of territory may be known and preserved.
[1913 Webster]
2. Any conspicuous object on land that serves as a guide;
some prominent object, as a hill or steeple.
[1913 Webster]
3. A structure that has special significance, such as a
building with historical associations; especially, a
building that is protected from destruction or alteration
by special laws intended to preserve structures of
historical significance; as, a landmark preservation law.
[PJC]
4. An event or accomplishment of great significance; as,
Brown v. Board of Education was a landmark of the civil
rights movement. Also used attributively, as a landmark
court decision.
[PJC]
{Landmarks of history}, important events by which eras or
conditions are determined.
[1913 Webster]