Definitions of bittersweet:

• noun:   twining shrub of North America having three-valved yellow capsules enclosing scarlet seeds
• noun:   poisonous perennial Old World vine having violet flowers and oval coral-red berries; widespread weed in North America
• adjective:   tinged with sadness

  Example: "A movie with a bittersweet ending"

• adjective:   having a taste that is a mixture of bitterness and sweetness