芳 means 'fragrant' - aromatic compounds were named for their pleasant smells. 烃 is the general word for hydrocarbon, coined from 碳 (carbon) + 氢 (hydrogen). So 芳烃 literally reads as 'fragrant carbon-hydrogen' = aromatic hydrocarbon.
register
Specialist chemistry term. The everyday word for 'fragrance' is 香味; 芳 is now mostly bound to scientific compounds (芳香, aromatic) and given names.
