landmark in WordNet English dictionary

1. an anatomical structure used as a point of origin in locating other anatomical structures (as in surgery) or as point from which measurements can be taken
   landmark 
   
2. a mark showing the boundary of a piece of land
   landmark 
   
3. an event marking a unique or important historical change of course or one on which important developments depend
   "the agreement was a watershed in the history of both nations"
   landmark  turning point  watershed 
   
4. the position of a prominent or well-known object in a particular landscape
   "the church steeple provided a convenient landmark"
   landmark