The story
From triangular + -ene (“benzenoid/graphene”). From being a triangle composed of benzene rings.
Etymology from Wiktionary, CC BY-SA 4.0.
triangulene
Today it means: A flat hydrocarbon graphene fragment, C₂₂H₁₂, composed of six fused benzene rings in a triangular configuration; being a radical having two unpaired electrons. Full definition →