1. a railway bridge over the Firth of Forth near Edinburgh . It was built in 1890 and is considered one of the greatest engineering achievements of its period. Most British people know the story that it is always being painted, because when the painters have finished painting it from one end to the other, it is necessary to start at the beginning again:
Tidying up after the children is like painting the Forth Bridge.
2. a road bridge that was built beside the Forth rail bridge in 1964. It is a suspension bridge (= a bridge hanging from cables supported by towers at each end) and one of the longest of its kind in the world.