/ ˈlændmɑːk; NAmE -mɑːrk/ noun
1.
something, such as a large building, that you can see clearly from a distance and that will help you to know where you are :
The Empire State Building is a familiar landmark on the New York skyline.
2.
landmark (in sth) an event, a discovery, an invention, etc. that marks an important stage in sth
SYN milestone :
The ceasefire was seen as a major landmark in the fight against terrorism.
a landmark decision / ruling in the courts
3.
( especially NAmE ) a building or a place that is very important because of its history, and that should be preserved
SYN monument