A leitmotif is a recurring image, phrase, idea, object, or sound pattern that returns throughout a poem or a body of poems and helps tie the work together. Each return can deepen the reader's sense of the poem's central concerns, such as memory, loss, or love.
Unlike a general theme, a leitmotif is something specific the poet repeats in recognizable form.
Example
The key in the drawer,
the key in the rain,
the key I keep finding
and losing again.
[n] a melodic phrase that accompanies the reappearance of a person or situation (as in Wagner's operas)