A HYDROCARBON is an organic compound composed of only hydrogen and carbon atoms. The term 'HYDROCARBON' can refer to a wide range of molecules, from simple alkanes to complex aromatics. The crossword solution for the term 'A HYDROCARBON' is TOLAN, which is an acronym for 'Tri-Oxygenated Linear Aliphatic Naphthalene'. This acronym is used to describe a specific type of HYDROCARBON, which is a linear aliphatic naphthalene with three oxygenated groups.