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Merriam-Webster Online Dictionary
landmark (noun)1.
an object (as a stone or tree) that marks the boundary of land
2.
a) a conspicuous object on land that marks a locality
b) an anatomical structure used as a point of orientation in locating other structures
3.
an event or development that marks a turning point or a stage
4.
a structure (as a building) of unusual historical and usually aesthetic interest , especially one that is officially designated and set aside for preservation