bittersweet nightshade
n.
A poisonous climbing or trailing plant (Solanum dulcamara) native to Eurasia and a widespread weed in North America, having violet flowers with recurved corolla lobes and red berries. Also called bittersweet, deadly nightshade.
[After the roots and stems, which are said to taste bitter, then sweet when chewed.]
bittersweet nightshadefruit (left) and flowers (right) of the bittersweet nightshade
Solanum dulcamara