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IUPAC nomenclature, from hen- (“one”) + eicosa- (“twenty”) + -ane (“alkane suffix”).
Etymology from Wiktionary, CC BY-SA 4.0.
heneicosane
Today it means: Any of very many isomers of the aliphatic hydrocarbon having twenty-one carbon atoms, but especially n-heneicosane CH₃(CH₂)₁₉CH₃ Full definition →