Nässelsoppa is asoup made of nettle leaves. Nässla is ‘nettle’, a common Germanic word, probably related to nät, net, as the fibres in the stems have been used to make thread to make nets or weave cloth. Brännässla, Urtica dioica – ‘stinging nettle’ is our most common member of the nettle family, Urticaceae. Urtica is an old Roman name of the plant, from urere – 'to burn' (transitive).
Dioica is a word constructed by Linnaeus from greek: dis – ‘two’ and oikos – ‘house’, to mean that the plants of a species are not bisexual – each sex lives in a house of its own, the female organs are placed in one plant and the male ones in another, just like in men and women. It’s a funny idea, to think of oneself as a house, isn’t it? (Learned from Jens Corneliuson, Växternas namn)