Heartbreak is a feeling of overwhelming sadness and grief. As Elvis sang, "Well, since my baby left me, I found a new place to dwell. Well, it's down at the end of Lonely Street, at Heartbreak Hotel."
Heartbreak can result from the breakup of a romantic relationship, or even the end of a platonic friendship — the heartbreak of having your best childhood pal move to another country can last a long time. The deep sorrow you feel when a loved one dies is an even more lasting and terrible kind of heartbreak. You can also use this word in an exaggerated way: "The soccer team's heartbreak was evident when they lost that match."