Deadly nightshade and Nightshade

Deadly nightshade noun - Poisonous perennial Old World vine having violet flowers and oval coral-red berries; widespread weed in North America.

Nightshade and deadly nightshade are semantically related. In some cases you can use "Nightshade" instead a noun phrase "Deadly nightshade".

Nightshade noun - Any of numerous shrubs or herbs or vines of the genus Solanum; most are poisonous though many bear edible fruit.

Deadly nightshade and nightshade are semantically related. Sometimes you can replace phrase "Deadly nightshade" with "Nightshade", this terms are similar.