tropylium
/trəʊˈpɪlɪəm/ /trəˈpɪlɪəm/Chemistry
noun
The cation C7H7 +, which consists of a planar ring of seven CH groups and has aromatic character. Chiefly attributive or as a formative element in chemical names.
Origin
1950s. From trop- + -yl + -ium.