Portend means to show a sign that something calamitous is about to happen. The teetering, tottering, pile of fine china piled up after the dinner party portends an imminent crash of broken plates and dishes.
Portend is a verb warning of omens, or bad signs. Dark clouds rumbling in over a county fair in Kansas portend the thunderstorm and even tornado that is likely to ruin the festivities. Portend is a helpful way for authors to foreshadow dark events ahead in their stories.