Deadly nightshade (Atropa belladonna) is a highly toxic hallucinogen. Its cousin, the black nightshade (Solanum nigrum) is partly edible.
Yes, The deadly nightshade is one of the most toxic plants found in the Eastern Hemisphere (though it has been introduced in the Western hemisphere). On the other hand, the ripe berries and cooked leaves of the black nightshade are used as food in some locales and selected plant parts are used as a traditional medicine.
Right. The botanicals are now sorted. So where does the name 'nightshade' derive from?
The Etymology Dictionary predictably claims that Old English nihtscada literally means 'shade of night'. Yes, both in Dutch and German the same word is used for these plants: nachtschade (Dutch) and Nachtschatten (German). The Dictionary suggests that the name is perhaps an allusion to the poisonous black berries.
A similar Swedish word was nattskata which meant a 'bat'. Even in Ancient Greek, 'bat' (νυκτερίς), derived from 'night' (νύξ). Bats were (and still are) shadows in the night.