In this poem, ‘bow’ means the rainbow.
The poet writes, “But the bow that bridges heaven, / And overtops the trees, / And builds a road from earth to sky”. Only one thing does all that — a rainbow.
The word bow means anything bent into a curve. A rainbow is a big curve of seven colours in the sky, so the poet simply calls it a bow.
- the curved stick used to shoot arrows — a bow and arrow;
- the ribbon tied in loops on a gift — a pretty bow;
- to bend the body forward to greet someone — we bow to our elders;
- the front end of a ship.