Saying in a soft, indirect or veiled way something harsh, ugly or forbidden to name.
In Paradise
so that I saw, beyond Gades, the mad passage of Ulysses, and on this side, near, the shore where Europa became a sweet burden
"Europa became a sweet burden" is the gentle way of saying she was carried off by Jupiter. The expression removes the harshness of the abduction and shows the way the poem speaks of a mythological violence, as one who points to a shore.