landmark

noun

1 the spire was once a landmark for ships sailing up the river:

marker, mark, indicator, guiding light, leading light, signal, beacon, lodestar, sign.

2 the Tower of London, one of London's most famous landmarks:

monument, distinctive/prominent feature, sight, spectacle.

3 the landmarks which separated the two states had been removed:

boundary marker, demarcator, boundary line, boundary fence, pale, picket;

Architecture terminus.

4 the ruling was hailed as a landmark by human rights activists:

turning point, milestone, watershed, critical point, historic event, major achievement;

crisis, divide.

landmark Oxford Dictionary of English